Hand Dug Well Manual (Abbott)

Hand Dug Wells :

Choice of Technology

and

Construction Manual

By Stephen P. Abbott

Hand Dug Wells: Choice of Technology and Construction Manual, by Stephen P. Abbott

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Table of Contents

Lists of Technical Drawings .......................................................................................................2

Glossary ..................................................................................................................................... 3

1. Introduction ............................................................................................................................ 6

2. Overview................................................................................................................................ 6

3. Design choices........................................................................................................................ 9

4. Pitfalls to Avoid.................................................................................................................... 14

5. Technical Preparation ........................................................................................................... 15

6. Construction Manual............................................................................................................. 15

Appendix AEquipment List for Hand Dug Well Construction .................................................. 37

Appendix B Specification for Hand Dug Wells ......................................................................... 43

Appendix C Bill of Quantities ................................................................................................... 53

Appendix DBibliography..........................................................................................................56

Appendix E Acknowledgements ............................................................................................... 58

Appendix F About the Author................................................................................................... 58


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Lists of Technical DrawingsYou may also view the techincal drawings via html pages.

Structural Drawings

The following links will open the structural drawings in PDF (Acrobat) FormatS-01 Caisson Lined Well S-07 Cover Slab with Pump and Acc Cover

S-02 In-situ Lined Well, Most Common S-08 Cover Detail (110 cm)

S-03 In-situ Lined Well, Variation 1 S-09 Cover Detail (150 cm)

S-04 In-situ Lined Well, Variation 2 S-10 Access Hole Extension

S-05 Caisson Ring Detail S-11 Access Hole Cover

S-06 Cover Slab with Access Extension S-12 Drainage Detail

Shop Drawings for Special Equipment

The following links open the Shop Drawings in PDF (Acrobat) FormatS-05 View of a finished Caisson E-08 Caisson Binding Rod Assembly

E-01 Caisson Mould Assembly E-09 Binding Rods and Pegs Details

E-02 Caisson Inner Mould E-10 Light Lifting Head Frame

E-03 Caisson Inner Mould Inserts E-11 L. L. Head Frame Side and End Rails

E-04 Caisson Outer Mould E-12 L. L. Head Frame Tower & Platform

E-05 Base Plate Detail E-13 L. L. Head Frame Crank and Roller

E-05a Methods for Forming Base Plates E-14 L. L. Head Frame Brake Assembly

E-06 Capping Ring Detail E-15 L. L. Head Frame Brake Components

E-06a Methods for Forming Capping Rings E-16 Tripod Components

E-07 Caisson Lifting Bar

http://www.worldbank.org/html/fpd/water/topics/tech/drawings/S01.pdf













http://www.worldbank.org/html/fpd/water/topics/tech/drawings/E01.pdf





http://www.worldbank.org/html/fpd/water/topics/tech/drawings/E05A.pdf


http://www.worldbank.org/html/fpd/water/topics/tech/drawings/E06A.pdf











http://www.worldbank.org/html/fpd/water/topics/tech/list.html


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Glossary

Word Definition

Apron A concrete floor outside the head wall of a well. The apron provides arelatively clean environment around the well, and controls drainage ofspilled water away from the well.

Aquifer A water bearing channel or cavity in the soil or rock. Aquifers may berelatively open cavities, or consist of porous material with water moving inthe interstices.

Base Plate Bottom portion of a caisson ring mould, used to support the side forms,maintain circular shape and spacing, and to form the lower rebate edge.

Bedrock Horizontal layer of consolidated rock formation extending much beyondthe limits of the well.

Bucket Pump A device for lifting water with a bucket without the removal and reinsertionof the bucket.

Caisson BindingRods

Rods used to attach the bottom 3 - 6 caissons together duringconstruction.

Caisson LiftingBar

A device for lifting caisson rings. The bar is inserted into two holes in theinner surface of the caisson ring. A triangle of steel rod allows lifting withminimal stress on the bar.

Caisson Ring Also Caisson or Ring; A cylindrical liner, usually pre-cast concrete orsteel, which may be placed in an existing hole, or sunk in place byundercutting or other methods.

Caisson Sinking A method of well digging consisting of undercutting pre-cast liners(caissons) to lower them in place and concurrently deepen the hole.

Capping Ring The upper portion of a caisson ring mould, used to maintain circularshape as well as form the upper rebate edge.

Concrete A mixture of portland cement, sand, and gravel. Other additives aresometimes used.

Contamination Introduction of pathogenic organisms or toxic chemicals into the water.

Cutting Ring A ring placed below the caissons to facilitate undercutting and sinking.Usually of concrete, it should have a concave bottom surface, and aslightly greater outer diameter than the caissons. It is usually notnecessary if the caissons are suitably designed and used.

DestabilizedSoil

Soil which has been disturbed, and is therefore at risk of collapsing orwashing into the well.

Digging Hoe A short handled broad hoe, approximately 20 cm square, with 65 -70 cmhandle at right angles to the blade. Called a Powerah in India, it alsoexists in many indigenous forms in Africa, Latin America, and some partsof Europe.

Drawdown The amount the water level is reduced below the static water level, at a


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given pumping rate.

Drilled Wells Wells constructed with a variety of rotary and percussive mechanisms,usually power driven. Drilled wells may have diameters as little as 5 cm,or as large as 90 cm, but are more commonly between 10 and 30 cm.

Ground Water Water which has been stored and filtered in the soil and rock below thesurface. Such storage and filtration usually results in purification frombiological contaminants. Sub-surface flows may however result inbiological contaminants being carried to a well in groundwatercontaminated by the mixing of surface water or other contaminants atsome distance away.

Hand Dug Wells Wells excavated and lined by human labour, generally by entering thewell with a variety of hand tools. They may be as small as 80 cmdiameter, and in some traditional cultures, as large as 15 metresdiameter.

Hand Pump A device for lifting water from the well without the use of buckets andropes, and powered by human labour.

Head Frame A structure placed over the well to prevent loose articles or soil beingknocked in, to support a working platform, and usually to support a liftingapparatus such as pulley or windlass.

Head Wall The portion of the well liner which extends above the ground level orabove the surface of the apron.

In-Situ Lining Casting a lining in place between the soil and an inner mould.

Lifting Calipers Devices used to grip the top edge of a caisson ring for lifting purposes.

Lifting Holes Holes left part way through the caisson wall to attach lifting bar or bindingrods.

Light LiftingHead Frame

A combination of a protective head frame with a windlass for lifting andlowering material and sometimes workers

Logging The process of recording the soil and rock conditions, aquifersencountered, and other relevant data on the well construction which maybe of relevance in contract administration, maintenance, or in constructionof other wells.

Modern HandDug Well

A well with improved depth, yield, lining materials, surface drainage,and/or other enhancements.

Moulds Forms used for casting shapes such as caisson rings from concrete.

Perforations See Weep Holes

PermeableMixture

Porous Concrete mixture. It is unnecessary and dangerous in the case ofcaisson lining.

Rebate Edge Overlapping joint edge of a caisson ring or culvert tile, used to assurebetter alignment of one segment with the next. Does not provide a watertight joint unless cement is used to join the segments.


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Shuttering Inner moulds used in in-situ casting of lining, or a temporary liner tosupport soil during excavation.

Soil Overburden The layers of various soils encountered above bedrock.

Spawl The tendency for surface layers of concrete to chip off and break awayfrom the main body of concrete. One common cause for this is thecorrosion and consequent expansion of reinforcing steel.

Static WaterLevel

The level of the water in a well that has not been recently pumped. It isnormal for the SWL to change seasonally.

Surface Water Water consisting of surface flows and therefore bearing surfacecontamination. If drainage conditions are not suitable, surface water mayfind its way into the well.

Tripod A three-legged structure used for lifting heavy loads such as the weight ofthe caisson ring. The tripod is usually combined with lifting devices suchas winches or block and tackles.

Undercut Of caisson rings, the process of deepening the well by sinking thecaissons as the hole is deepened.

Unstable Soils Sands, silts, and other soil mixtures which may flow or collapse when oneside is unsupported.

Weep Holes Holes formed all the way through concrete liners to permit the free flow ofwater. In the case of pre-cast or caisson linings these are usually notnecessary.

Well Cap Usually a round concrete slab used to cover the well. The cap must besuitably reinforced. Pump mounting bolts and access hatches are castinto the cap as appropriate.

Well Head The structural components of the well above grade level. Ie. Apron, HeadWall, Cap, and drainage.

Winch A lifting device intended for greater lifting capacity combined with slowermotion. May consist of a drum to wind cable, linked to a crank through agear mechanism to achieve greater mechanical advantage.

Windlass A lifting device consisting of a cylinder to wind rope on, and a crankmechanism. Usually has a light to moderate lifting capacity combinedwith relatively fast motion.

Yield The quantity of water that can be drawn continuously from a well. Theyield, measured in litres per minute, or gallons per hour, must normally bespecified at some acceptable drawdown.


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1. IntroductionThere are several excellent books and articles about well digging, which were written in the1960s and 70s.1 With great appreciation for these works and their authors, we undertook thiseffort to provide some practical guidance on the choice and completion of technologiesintroduced in those documents.

A few important techniques and tools have been left out of the previous books in the field.Additional information is needed on the caisson sinking component, which is needed forcompletion of most improved yield wells. Giving credit where credit is due, those early textsvery amply cover the topic of in-situ lining, while we barely mention it, leaving that topic insteadto those who know it best.

Most of the earlier books were written as a sort of anthology of the various methods in use.Several construction methods were included which are not the most practical approach, andwhich are damaging to the finished wells, and/or dangerous for the diggers. Relatively littleguidance was provided for choosing technologies, and even less guidance for mixing andmatching components. In this document, we point out some necessary choices among thesetechnologies and some of the pitfalls of inappropriate combinations.

We present designs for some of the essential equipment, optimised for durability, safety, andlower cost. These include; simpler, cheaper, more flexible, and surprisingly more durablecaisson moulds, along with a light lifting head frame, a tripod, caisson lifting apparatus, andcaisson binding rods.

Similarly the caisson wall thickness is optimised to avoid structures that are too heavy to bemanipulated safely, or too thin to be easily reinforced without exposing the rod.

The author hopes that this contribution will help to resolve some of the problems and frustrationsencountered by those attempting to use the caissoning methods in recent years with insufficientinformation.

2. Overview

2.1 A Brief History of the Modern Hand Dug WellHand dug wells have been used by humanity since before recorded history. Most civilisationsthat needed them had, and many still have traditional methods for well digging. In modern timessome of the methods, equipment, materials, expectations, and standards for well constructionhave been improved to allow better and more permanent yields, depths suitable for modernpumping, and better protection from contamination.

Between the early 1930’s and today, the dug well has evolved in some places from minimal,unlined holes to concrete lined structures with specified depth and yield, and with improvedheadworks and drainage.

A brief chronology includes the following:

1 Two of the most notable examples are “Hand Dug Wells and their construction”, by S.B.Watt andW.E.Wood, and “Wells Construction”, by Richard E. Brush. The Bibliography contains a more complete list.


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• Africa; 1930’s; In-situ cast concrete linings to avoid collapse and to excludecontamination. Other lining methods included bricking and stone masonry.

• India; early1950’s; Caisson lining methods to meet the need for simpler and lowercost construction technologies. Entire wells were lined by this method.

• India; early1950’s; Caisson sinking as a very effective method of deepening wellsbeyond unstable soils and beyond the water table.

• Africa; 1960’s and 70’s; Caisson lining methods to deepen wells that were mostlybuilt with in-situ cast linings. Much of the caisson sinking method was lost in thetransfer. Not much was done to rediscover it, as the writers of the time, and the usersof the recent past did not realise the technology was missing.

The concept of the modern dug well, evidently changes with time, and with our own priorities.For most workers in the field it now includes: durable liners, usually of concrete; ample depth,achieved through caisson sinking techniques; improved yield, resulting from the greater depth;and improved headworks and drainage.

2.2 Comparison: Unlined vs. Caisson Lining vs. In-situ with Caisson FinishingLining Method Unlined Well In Situ Cast,

Caisson FinishedCaisson Lined Well

Contamination Almost impossibleto exclude due tolack of headwall.

Can be preventedwith suitablebackfill, headwall,apron, drainagechannel, and accessmethod.

Can be preventedwith suitablebackfill, headwall,apron, and drainagechannel, and accessmethod.

Depth Usually small due tolack of stability.

Final depth dependson finishing bycaisson sinking.

Final depth dependson continuation ofcaisson sinking.

Volume of excavation May be very largedepending on soilinstability

1.76 m3 / metre ofdepth.

0.95 m3 / metre ofdepth.

Volume of concrete Not applicable 0.5 m3 / metre ofdepth (in addition toheadworks).

0.25 m3 / metre ofdepth (in addition toheadworks).

Labour required Variable dependingon depth

Approx. 4 – 8Person days permetre of depth

Approx. 2 - 3 Persondays per metre ofdepth

2.3 Comparison of Dug Wells (lined) with Drilled Wells or BoreholesIn some societies the modern dug well has gone almost unnoticed as the convenience of drilledwells came on the scene too soon. Drilled wells offered fast, standardised, relatively predictable


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results. Unfortunately they were also relatively expensive, and the necessary skills andequipment were not available at the community level.

Drilled wells have also led to some very wrong conclusions about the availability of groundwater. Drillers trained to exclude water encountered in the soil overburden have logged the firstsuitable aquifers as being many metres below the surface of bedrock. In many instances this hasled engineers and project administrators to conclude that dug wells were not feasible. In someinstances it was later noted that large numbers of traditional dug wells already existed in thesame area.

Drilled Well (Borehole) Modern Hand Dug Well

Typical Cost $5,000 - $12,000 $400 - $1,200

Typical Depth 15 m – 90 m Typical 8 m – 15 m Typical

6m – 25 m Effective limits

Water Quality Greater chance of Salinity problems Slightly greater chance ofcontamination

Access toWater

Requires hand pump or high techpumping and power source

Allows full range of access andpumping options.

CommunityInvolvement

Very low; Might involve attendanceat some meetings arranged byoutside animators

Typically high; May involveplanning of site, contribution ofcost, contribution of material,contribution of labour, directparticipation

SmallContractorInvolvement

Usually involves only largercontracting firms due to high capitalinvestment; $200,000 - $400,000

Can involve very small firms andindividual contractors, sometimesthrough hire/purchase of equipment;$500 - $2,500

What dug wells can do is access the water found in relatively shallow aquifers above thebedrock, and to a lesser extent, in the upper layers of bedrock. In our experience this is oftenmore successful than drilled wells.

Because of their larger diameter, dug wells can be used where a community is unable to afford apump. With suitable design, windlass, bucket pumps, or a variety of other low technologypumps can be used in place of a commercial hand pump.

Dug wells encourage entrepreneurial construction at a local level, owing to very low capitalinvestment requirements. Because they are easily replicated, they place the project control backin the hands of village elders and civic minded individuals.

2.4 Caisson sinking at the heart of the hand dug wellCaisson sinking is one essential that makes improved and more consistent yields possible.

In parts of Africa where shuttering and pouring of concrete liners were introduced in the 1930's,caisson sinking has been added to that technology to make greater yields possible.


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In India where caisson sinking was introduced in the 1950's and 1960's as a method of wellconstruction from the “ground down”, it remains the most successful method of digging modernwells.

Caisson sinking is a method of deepening the well safely through unstable soils. It can also beused in stable soil conditions, and is the more effective for having been started before problemsof instability developed. In addition to providing an efficient, permanent, cost-effective liningmaterial, it stabilises the well shaft, protecting the workers and the well itself during excavation.Achieving these benefits, however, depends on provision of the necessary tools and equipment,quality of the caisson moulds themselves, and on the training of the diggers.

2.5 The need for basic training in caissoningIt is important to recognise the key role of caisson sinking, especially in designing trainingprogrammes for well diggers. When used in combination with other technologies such asshuttering, the caisson sinking is done at the end of the digging process. It is therefore treated asa supplementary and trivial technology rather than the most important activity of all. A commonfeature of intensive training programmes for well diggers, is that there is so much to teach andlearn that the "supplementary or trivial" gets postponed until the last half-hour. At this point theinstructors say something like "...and then you put in the caissons, disinfect the well, cap it andyou are finished". This trivialisation can lead to disappointing and sometimes disastrous results.

If the methods of sinking caissons are not clearly understood or the appropriate equipment is notprovided, then the caissons are worse than useless. We have met well diggers who detestedcaissons, because they thought they were to dig through the unstable conditions below the watertable and then lower the caissons into the hole before it washed in. This usually can not beachieved. What is worse, it makes it difficult or impossible to centre and level the caissons, andcreates a serious risk of caving in the well shaft. Others delayed putting the caissons in placeuntil far too late even though they knew the risks, because they had never tried sinking them withthe appropriate tools. It is virtually impossible to fill a bucket with soil, with a long shovel,inside a caisson ring, especially under water. With a digging hoe, however, it is easy.

2.6 The efficiency of caisson lined wellsThe ultimate efficiency of caisson lining methods is dependent on having the correct equipmentand training. We have seen caissoning completely stalled due to lack of equipment andunderstanding. We have also seen wells constructed entirely with caissons, in less than ten dayswith 3 workers, where an equivalent well with in-situ cast lining would take about two monthswith a crew of 5. What is more important, it is done much more safely with the caisson sinkingmethod.

3. Design choices

3.1 Upper segment lining methodsAs has been noted above, the choice of technology for the intake section of the modern hand dugwell is relatively fixed. If the intake is to be deepened enough below the water table to ensure acontinuous and dependable source in all seasons, or to allow the installation of a pump, then


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caissons will usually be needed. In the top section of the well, there exist other choices, althoughthe author of this manual has his own preference, as will be made clear below.

3.1.1 Caissons all the wayWhen suitable preparations are made, there is aconsiderable advantage in using the same liningmethods for the whole well as is eventually plannedfor the intake section. Caisson sinking provides asafe working environment, a superior and very costeffective method of lining, and simpler and lesscostly equipment purchase. Using only the onetechnology also allows a simpler, more concise anduniform training curriculum. Caisson sinking, anessential for the completion of the well, is a skillwhich must be taught in any case, but has oftenbeen neglected in the past owing to the perceivedneed to teach the in-situ casting technique first. Inmuch of India and in other parts of the world wherecaisson sinking has been taught as the primarymethod of lining, there is no compromise of safetyin digging an unlined, unstable shaft and thenlining it. There is no trade-off between preliminarylining techniques and finishing techniques.

To those not accustomed to the sinking of caissons,there are a variety of disadvantages in the caisson

sinking method, including the need to work in a moreconfined space and the need to manoeuvre the heavycaissons, both on the surface and down the well. Oftenthe workers prefer to work in the larger diameter of theunlined hole used with in-situ casting, but this attitudeis largely dispelled when the correct digging tools areintroduced.

3.1.2 In-situ castingIn-situ casting of the well liner is another method ofplacing a concrete liner in the well. In this method, theundisturbed soil of the outside of the hole is used as theouter mould. Shutters, or inner moulds are assembledin the well, centred, and levelled, and then the spacebetween them and the wall, is filled with concrete.There are several disadvantages with this technique:

In the first place, digging must be stopped while thecasting takes place. There is always the temptation todelay the casting a little longer and continue digging inan unlined shaft. The material requirements are much


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greater, as the wall thickness is greater, and the inner diameter must be large enough to permitthe insertion of caisson rings through the upper section lining. Each section cast in place must bepoured below the previous section, which creates problems in filling the moulds, and particularlyin joining each successive section to the previous section above it. Lower sections cast inunstable soil have been known to break free and fall in, especially after unstable conditions areencountered below them.

There is a larger volume of soil to be removed owing to the larger finished diameter, andincreased wall thickness. The walls must be cut very precisely, or else strength and materialsmay be sacrificed owing to the uneven wall thickness.

3.2 Caisson and cutting ringsSuitable design of caissons and where applicable, cutting rings, is essential for purposes ofeconomy of materials, productivity, and above all, safety. A caisson ring with an OD of 110 cm,a wall thickness of 7 cm, and height of 60cm is light enough for three to four workers tomanipulate. It is large enough for the same number to tip or roll safely in most environmentswithout getting in each other’s way. Increasing the wall thickness to 10 cm makes its weight toogreat to be manipulated by the number of people who can safely gather around it. This is oneinstance where thicker is neither safer nor more durable. One well digging project in Sri Lankahas successfully demonstrated that the caisson walls can safely be reduced to 5 cm, but we do notrecommend this extreme reduction owing to the increased precision required in placement ofreinforcing materials.

If rebate edges are used, then the caisson rings should be inserted with the narrow rebate edge atthe top. This creates a natural filter in each joint and stops flows of sand and silt from enteringthe well, but more importantly, it makes it very much easier to undercut the ring without the useof a cutting ring. Some early illustrations of caisson rings with rebate edges presented in WestAfrica, showed the caissons inverted. Lacking any contrary information, these illustrations havebeen followed almost universally in thearea, causing very serious problems.

Suitable moulds for producing the rebateedges have not been generally available inthe past, and very poor substitutes havebeen commonly used, further complicatingthe difficulty of using this form of caisson.The use of base plates and capping rings,an innovation which allows the productionof a more suitable rebate edge is describedin the next section of this document.

There is almost never any need forperforations of the caisson rings or for theuse of permeable mixtures of cement. Thewater enters easily through the jointsbetween caissons and from the bottom.Some workers in the field have speculatedon the need to use porous caissons in the


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intake section of the well. Such misconceptions likely result from the very real need for thesemeasures in the case of In-Situ lining. In India in the 50's and 60's, only solid concrete caissonrings were in use for well construction. We are not aware that the water ever had any difficultyentering the wells.

Those who felt it necessary have tried both porous concrete, and weep holes cast in the caissonwalls. We do not encourage the use of either of these solutions, as one weakens the concretedrastically and can cause spawling due to corrosion of the reinforcing rod, and the other vastlycomplicates and increases the cost of the necessary moulds. If designers insist on using porouscaissons, however, we suggest they opt for the use of weep holes, as the use of porous concrete isfar more dangerous.

If the caisson moulds are sufficiently accurate, and rebate edges are correctly oriented, then thereis usually little or no need for a cutting ring. If cutting rings are used, there are several designprinciples to be followed in order to avoid serious problems: The outer diameter of the cuttingring may be made about 2 - 3 cm greater than that of the caisson rings, but must not be mademore than this. Too great a wall thickness of the cutting ring makes under-cutting much moredifficult, and perhaps more importantly, creates a thick layer of destabilized soil which is verydifficult to restabilize if a flow should start on the outside of the caissons. The tapered edge ofthe cutting ring should be steeply inclined, and be concave rather than convex.

The caisson moulds presented in the shop drawings allow the outer mould to be made larger bythe insertion of a wooden block in one or both of the joints. The base plate and capping ringeach include a secondary seat to fit the enlarged outer mould, in order to make a cutting ring onthe same mould that forms the rest of the caisson rings.

3.3 Caisson mould designCaisson moulds were not always as complicated in design as they have become in recent years.In India, in the 1950s, caisson moulds were introduced that were made of simple hoops of 14gauge or 2 mm steel sheet, with the ends bent at 90 degrees or angle iron riveted on to form boltflanges. These moulds were much more flexible than many of the more complicated stiffenedforms in the field today. Interestingly, the caissons were rounder with the old flexible forms, andthe moulds never wore out.

The stiffened forms that have been introduced since that time are generally not sufficientlyprecisely built to offer a rounder product, but they are much more costly to produce and muchmore vulnerable to damage owing to their rigidity and the weakness of welded joints.

A design for caisson moulds has recently been introduced, which takes advantage of the lowercost and durability of flexible moulds, combined with rigid rebate edge moulds incorporated intoa base plate and capping ring, to offer much rounder products. Draughtings of these moulds arepresented in theEquipment Shop Drawings, Section 5.5.

3.4 Other useful equipment See Equipment Shop DrawingsDesigns for several additional pieces of equipment are presented in the shop drawings:


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The Tripodis optimised for size and strength.This means that it is not only strong enough tolift two or more caissons together withoutbuckling, but it is light enough to be erectedsafely by three or four workers, and largeenough to operate over the head frame.

The Light Lifting Head Frameprovides awindlass, with sufficient mechanical advantageto safely assist a worker from the bottom of thewell, a convenient working platform over thewell, and a frame around the well to preventobjects from being accidentally knocked into theexcavation. The legs on the inactive side of theframe are sufficiently long to allow the windlasscomponent to slide out of the way and stillprovide protection and support as the caissonrings are lowered through it.

Caisson Lifting Baris a light weight triangularstructure which attaches to the two lifting holesin the upper inside walls of the caisson ring tolift it. It fastens positively and yet flexibly tothe caisson. It also causes less stress on thecaisson itself than other devices like liftingcallipers, for instance.

Caisson Binding Rodsattach the bottom 3 to 6caissons together to avoid separation duringdigging. These rods take advantage of thesame lifting holes used by the caisson liftingbar.

3.5 Well head design See Structural DrawingsThe well head structure consists of the head wall, well cap, and apron. Depending on the wellcap design, it may also include an access hatch cover, and / or an access hatch extension. Thedesign presented here comes in two variations depending whether it is to be applied to a 1.5 mOD In-Situ cast well liner, or a 1.1 m OD caisson type well liner. The design is intended toprovide maximum flexibility between the use of a hand pump, or the need to access the well foroccasional maintenance or for regular use of a bucket. It may be seen that specialised moulds areneeded to produce the pump base, the access hatch lip, the access hatch extension, the access


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hatch cover, and possibly the apron.

4. Pitfalls to AvoidA series of problems resulting from inadequate specification, or through the application ofinappropriate designs to caisson lined wells:

Where someone drew the caissons the wrong way up...

In West Africa, two visiting European engineers in 1989 introduced a drawing of a well withcaisson rings at the bottom. The caisson rings were shown upside down. That Drawing waspassed from agency to agency as a national hand dug well program was introduced in thatcountry. Very many caissons were fitted upside down in about the next seven years. Amongother problems, this made the caissons near impossible to sink without the use of a cutting ring.

But if the cutting ring design too was wrong...

The drawing of a cutting ring, most readily available, was one intended for use with caissonsconstructed from “H-blocks”, which are much thicker than a simple concrete caisson. Theadditional thickness and poor contour that resulted from the use of this design, madeundercutting of the caissons about five times as difficult as it might have been if the caissons hadbeen fitted the right way up in the first place. Worse still, the cutting ring destabilized a muchgreater thickness of soil on the outside of the caissons than is normal, with the result that whennaturally unstable soils were encountered, it was far more difficult to cause the flows to settle outand restabilize.

And materials specifications are copied over from another lining specification entirely...

One of the techniques which may be necessary in in-situ casting of linings, that is totallyunnecessary in the case of caisson linings, is the use of concrete with little or no sand in order toproduce a porous wall. When this method is replicated in the case of pre-cast caissons, theresulting weakness and instability is a serious hazard for the workers.

When the project provides or specifies the wrong tools...

The shovel or spade, which is only a moderately usable tool in the large diameter hole excavatedfor in-situ lining, is completely unsuitable for caisson sinking. The handle of the shovel can notbe tipped down in order to lift the soil to the bucket. In northern Ghana, one contractor showedoff an incomplete “improved well”; incomplete because he could not cause the caissons to sinkwith the spade and pickaxe provided. The same contractor “moonlighted” digging traditionalwells, about 80 cm diameter when lined, using the traditional local digging hoe. He wasextremely successful and efficient in completing the traditional wells because he was using hisown tools. Foremost among these was the digging hoe!

And so forth...

The list of case histories could go on much longer, but the point of all of this is to review ourassumptions in the field. As an administrator or engineer sitting at a desk we can not easily seethe results of our choices, and they may not be reported back to us for many years. We need toremain vigilant for errors. There is a significant lack of guiding literature on caisson lining andcaisson sinking techniques, and there is great danger in simply adopting the technologies usedwith other lining methods, for use with caissons.


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5. Technical PreparationThe following sections are prepared on the assumption that dug well construction is to be

organised on a regional basis.

5.1 Equipment ListsWhether from the point of view of project management for a regional programme, or of acontractor or entrepreneur, it is equally critical that the correct equipment purchases be made.The attached lists are intended to facilitate appropriate selection of tools and equipment. SeeAppendix 1.

5.2 SpecificationsA set of precise and clear specifications is a prerequisite for bidders to respond realistically andcompetitively to the requirements of the Employer without qualifying or conditioning their bids.They serve to present a clear statement of the required standards of workmanship, materials, andperformance for the goods and services to be procured.

Appendix 2presents a sample set of Specifications for procurement of well digging services.

5.3 Bill of QuantitiesThe objectives of the Bill of Quantities are as follows:

a. To provide sufficient information on the quantities of Works to be performed toenable bids to be prepared efficiently and accurately, and;

b. When a Contract has been entered into, to provide a priced Bill of Quantities foruse in the periodic valuation of Works executed.

Appendix 3presents a sample Bill of Quantities format

6. Construction Manual

6.1 Safety IssuesA general awareness on the part of the diggers and the site co-ordinator, of the hazards in andaround the well is probably the most important requirement for the operation of a safe site. Aknowledge and continuous awareness of well site organisation, discussed in the next section, isalso crucial in preventing accidents. A basic knowledge of first aid, and apractisedskill in theemergency evacuation of a casualty from the well are very important. Finally conscious andserious concentration on the job and avoidance of casual or joking behaviour on the work sitemay save lives.

Appropriate equipment is equally important to prevent accidents and mitigate the effects of bothmajor and minor emergencies when they do occur. Suitable design of light and heavy liftingequipment for the routine raising and lowering of buckets as well as for the heavy tasks ofmanipulating caisson rings will greatly reduce the risk of accidents. Protective clothing,especially a suitably designed helmet, is very important. First aid equipment and escape and


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rescue equipment are needed on site in case of minor and major accidents.

6.1.1 Hazards of dug well constructionFalls and falling objects

The risk of serious accidents at the well site as well as the more minor cuts and bruises canusually be avoided through understanding the situations that can lead to such misadventures.

Poor organisation of the well site can lead to numerous mishaps including loose objects beingknocked in upon the worker at the bottom. The next section of this document presentsrecommendations for avoidance of such mishaps.

Inattention while assisting from above can result in objects or workers falling into the well,possibly through loss of control of the rope or lifting head frame. While quiet good humour onthe job is desirable, loud or boisterous behaviour on the part of the workers should be forbidden.Other distractions and casual visitors should be avoided. A brief discussion on mood andbehaviour around the well site is provided in the section on site organisation.

Exhaustion of the workers can lead to serious falls while entering or leaving the well. Suchexhaustion must be avoided, but also the preparations for entering and leaving the well should besuch that even an exhausted or injured worker can get out or be assisted out without risk.Suitable design of the light lifting head frame allows workers at the top to lift the weight of aworker leaving the well without loss of control. Various forms of ladders are used for entering orleaving the well unassisted. These need to be suitably constructed to be easily gripped even inwet or slippery conditions. Rope ladders are not easy to use when one is exhausted. They can beimproved considerably by suitable design and careful construction. Keeping the rungs smallenough to fit comfortably in the fist and keeping the rungs exactly parallel, for instance.

Moving heavy objects

One of the serious hazards of well construction results from the need to manipulate heavyobjects, most particularly pre-cast caisson and cutting rings. A part of the risk can be eliminatedby the provision of suitable heavy lifting equipment.

In many instances we have encountered heavy lifting apparatus that was so heavy and unwieldythat it increased the risk of accidents.

A careful design can prevent much of the hazard, by balancing minimal weight with the neededstrength. Oversized caisson rings concentrate so much weight in one place that sufficientworkers to manoeuvre or lift one side of the ring are unable to gather safely around it. Reducingthe diameter to 110 cm OD, and the wall thickness to about 7 cm, results in a caisson ring thatcan be safely tipped up, rolled into place, and tipped down at the edge of the well, by about threeto four workers without interfering with each other.

Suitable design for both caissons and heavy lifting apparatus are discussed in the section entitledDesign Choices, and further illustrated in theEquipment Shop Drawings.

Air Quality

Poisonous gasses are occasionally found to occur naturally in deep excavations, but far morefrequently they result from engine driven pumps, generators, or compressors used at the wellsite. Carbon monoxide laden exhaust is heavier than air, and therefore sinks down the well,


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pooling at the bottom. It is not sufficient only to avoid placing engines in the well. They shouldnot be operated upwind of the well, or within about 8 metres in any other direction.

Workers should always enter the well with caution, mindful of any odours, malaise, or weaknessthat they experience. The team members above should also remain vigilant to assist the worker inthe well without delay when needed. Any rescuers entering the well in the case of unexplainedweakness or loss of consciousness should remain attached to a safety line themselves in casethey should also succumb. See the section on escape and rescue.

When the air quality is known to be poor in an excavation, blowers can be used with flexiblepolyethylene duct to carry fresh air to the bottom.The blower may be as simple as a manuallyoperated forge blower. If a blower is found to benecessary, it should be operated continuously byone full time worker who can both crank thehandle, and also ensure that no kinks or blockagesoccur in the flexible duct.

6.1.2 Equipment for SafetyA responsible contractor will ensure that theappropriate safety equipment is at site and in use.In some instances the right choice of equipmentincreases production, as is the case with the liftingapparatus. In other cases careful purchasing willprevent impediments to production, as is the casewith the climbers' helmet. In all cases they willavoid work stoppages, prevent needless sufferingand loss of life or limb, and incidentally ensure agood record for the contractor him/herself.

6.1.3 Light and heavy lifting apparatusA well built light lifting head frame or “windlass” provides fast,safe efficient means of lifting soil, tools, and even personnelfrom the bottom of the well. In addition the frame provides asafe platform for the workers, and a protective wall to avoiddropping rocks, soil, or tools in on the worker below. See thedesign of the head frame, E-10, in theEquipment ShopDrawings.

A tripod and winch are used for lifting and manipulating heavyobjects such as caisson rings, into the well. The tripod shouldbe appropriately sized for both strength and convenient use. Forstrength the height should be limited, and the legs should be ofgood quality 2" or 2.5" galvanised pipe. For convenience of usethe height and weight should be such that three men can safelyerect and move it. The winch must be appropriately sized toenable lifting at least 500 kg without undue strain, yet light


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enough and fast enough to avoid discouragement with its use. See the tripod design, E-16 in theEquipment Shop Drawings.

If the tripod and windlass are built to the optimum dimensions then it is possible to operate eachwithout removing the other completely from the well. This is a great convenience and alsoincreases safety by removing the temptation to use the wrong lifting apparatus for any particularjob. The tripod also provides an additional anchor for ropes and pulleys in the case of rescueoperations.

6.1.4 Protective ClothingHelmet or hard hat

The helmet is the most critical part of the protective clothing. Acommon but unsuitable practice is to provide the workers withordinary construction hard hats. These fall off when working downthe well, and thus are only in the way. The most suitable design forwell digging is climbers' helmet. This is fitted with a chinstrap toavoid falling off at awkward moments. Climbers’ helmets may bedifficult to procure locally. They can be ordered from most sportinggoods stores that cater to climbers. Some other sports helmets mayalso be suitable. i.e. Lacrosse, hockey, handball, etc, provided thatthey are fairly compact and fitted with chinstraps.

Hearing protection

Where noisy equipment is used, particularly compressor driven breakers anddrills, hearing protection is very important. These can take the form ofearplugs or the headphone type ear protection. If earplugs are used, thenprovision should be made to replace lost or worn out plugs. They generallydo not last forever. If headphone type hearing protection is used, it mustintegrate well with the helmet.

Eye Protection

Safety glasses are essential where any chipping work is beingperformed. Open type glasses are better for this purpose, dueto the tendency for closed goggles to fog up in the well. Safetyglasses should have relatively large, shatterproof lenses.

Boots

Whether boots are appropriate protective clothing depends somewhat on cultural norms.Probably it is appropriate to provide wellington (rubber) boots. It is not uncommon for workersto request leather work-boots because they represent a greater bonus or have greater status. Thefeet are most vulnerable when working under water, and the leather work-boots do not serve inthat environment. Even with rubber boots it may be noted that the workers will remove theirboots to go down the well. This may be because they are used to working barefoot. If so, theymay in fact be safer in bare feet.


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Gloves

Gardening gloves or other work gloves may be provided. It is unlikely that they will be useddown the well, especially after water is reached. In any event rubber gloves should not beprovided, as they can not be kept dry inside, and only interfere with awareness of hazardousconditions.

6.1.5 First Aid KitWhen mishaps do occur, it is essential that a basic first aid kit be available on site. A suitablefirst aid kit would contain the following list of bandages and antiseptic solution.

Adhesive Bandages 25

Adhesive Tape 1

Sterile Gauze Compress 10

Gauze bandages 5

Triangular bandage 2

Iodine solution 1

Soap 1

Scissors 1

Tweezers (forceps) 1

First aid supplies should be replaced when used. If the kit is not checked regularly to ensure thatthe full complement of supplies is present, they will not be available when needed.

A supply of aspirin or other drugs is not an appropriate first aid kit, nor should it even beincluded in a first aid kit.

6.1.6 Escape and Rescue EquipmentLadders

Ladders have the advantage of enabling the down hole workers to get out of the well unassisted.They should never be seen as an excuse for not preparing to assist workers from the well. Badlydesigned or badly built ladders are a danger. Rope ladders in particular can be a serious hazard.

It is very important that the rungs of ladders be not only strong, but also sufficiently small indiameter to be firmly grasped in the fist of the climber. Eventually the workers will be climbingwith mud on their feet, and the resulting slime on the ladder makes it extremely hard to grasp thevertical parts or rungs that are too large to fit in the closed hand.

Rigid ladders may be provided for shallow wells. If they are used, it is particularly useful tofasten ladders to the side of the well, as this prevents the situation where they are removedbecause they are in the way, and must be replaced by workers above before the down holeworker can get out.


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Rope ladders can be provided for deeper wells, but it should be recognised that they are anadditional stress for an exhausted worker, generally encountered after he/she has already reachedthe limit of his/her endurance. Rope ladders must be manufactured from known materials. Therungs must be kept small, and therefore must be of strong wood. The ropes must be chosen frommaterials that do not stretch over time. The knotting and assembly of the ladders should be donewith great precision to avoid unequal or sloping steps, which can be extremely hazardous whenslippery.

Harness How to Make a Hasty Harness

How to Use a Hasty Harness

Two sets of rescue harness should be available at the well site, in order to remove exhausted,injured, or unconscious workers from the well. The harnessshould be easy to apply to oneself or to another person. Thereexist a variety of manufactured harnesses, but most of themare confusing and awkward to apply, especially to a casualty.

Fortunately the “hasty harness”, one of the easiest forms ofharness to apply to oneself or another person, is also one ofthe simplest and cheapest. It consists of two loops ofwebbing, which are applied as a seat harness around the legsand waist, and a chest harness crossed behind the back. It isimportant that all the workers at the site practice regularlyapplying the harness to themselves and to each other. This practice can be accomplished inconjunction with the lifting head frame, in the course of the digging work.

Extra Ropes

It is common to operate a well site with only one rope, which is normally in use to lift buckets ofearth during the digging. A second strong rope should be provided at the site for rescue purposes.A suitable length for this rope is roughly double the normal anticipated depth of a completedwell.

6.1.7 Mood and Conduct at the well siteThe conduct of any one worker can affect the safety of the whole team. Good humour on the siteis important, but excessive joking or casual behaviour is to be avoided. In the context of the wellsite, loud and boisterous behaviour is the same as careless behaviour. The results can bedisastrous.

When a worker is in the well, at least one supporting worker at the top should be engaged invisual contact and quiet conversation with them at all times. Loud or joking behaviour amongworkers outside the well impairs this essential contact. Workers at the well head and other partsof the work site should move with cautious efficiency, never run if it can be avoided.

Alcohol and drugs must be avoided at the well site at all cost. A worker who comes to workinebriated, or drinks or takes drugs at the site, should be sent home immediately. Work shouldstop until they are gone and a suitable replacement has taken their place.

Casual and untrained visitors at the well site should be avoided. If dignitaries, villagers, orsimply curious children come to the construction site, then the co-ordinator or a designated


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worker must take charge of their behaviour. They must explain the situation, either sendingthem away or showing them where they may safely stand or sit to observe without risk tothemselves or to the workers.

6.1.8 Well Site OrganisationGood well site organisation is as important for productivity as it is for safety. The illustrationshows one possible site layout. One important feature of the layout is to avoid over-crowding.


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Tidiness and cleanliness of the tools are equally important. Ropes should be coiled when not inuse, and tools should be stored a convenient distance from the well head in order to avoid thedanger of tripping or knocking objects into the well.

The supporting activities such as concrete mixing and casting of caisson rings should besufficiently far away from the well head to avoid crowding, and to allow safe storage of thecaissons while curing.

Safety equipment should be just as accessible as the production tools! First aid kits andrescue equipment are not adequately accessible if they are in a locked box when an emergencydevelops, therefore they should not be locked up during digging operations.

The well site organisation can deteriorate very quickly if it is forgotten. It should be a part of thenormal discipline of the site leader, and his/her team members, to review the organisation at eachrest break as well as at the start and end of each day.

6.2 Casting CaissonsCaissons can be cast on site, or at a central yard. Where there exist problems of access ortransportation, it is likely to be simpler to transport the moulds and materials to the site and castthe caissons there. If they are to be cast on site, then it is important to start early enough that asupply of sufficiently cured caissons be available when needed. Assuming that the caissons areto be added when the excavation reaches about 3 metres depth, and that the caissons should curefor about 6 days before lowering in the well, then the casting should begin about 4 days beforethe excavation.

It is important that the forms are cleaned, lubricated, and assembled, and that the reinforcingsteel be bent and ready before concrete mixing is begun. This is because much of the strength ofcast concrete can be lost if it is not used promptly when it is mixed. As a general rule theconcrete should be discarded if not used within 30 minutes after addition of the water.

The moulds are kept centred and round by assembling the inner and outer hoop mould on thebase plate (lower rebate edge mould).

Two hoops of 6 mm reinforcing steel, wired shut, are prepared in advance. For maximumbenefit they should be inserted roughly 50 mm above the upper surface of the lower rebate edge,and 50 mm below the lower surface of the upper rebate edge. Specially bent hooks of the samesteel can be used to keep the reinforcing hoops centred and at the right height.

After the lower reinforcing hoop is in place, then the pegs that form the lifting holes can beadded. At this same stage, if required (not recommended), the pegs to form the weep holes canalso be added.

Temporary spacer blocks are used between the inner and outer moulds during the filling, andremoved as the concrete level reaches them. The most convenient design for the spacer blocksconsists of 25 mm by 25 mm lumber cut to 12 cm lengths, with a saw cut placed 7 cm from oneend, so that the block can hang on the upper edge of the outer mould.

The capping ring (upper rebate edge mould) is added to the upper mould after it is filled to the


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lower surface level. The small amount of concrete needed to complete the upper rebate edge isadded through the gap remaining inside the capping ring.

The concrete should be made with fresh dry cement, and with clean graded aggregate and cleansand (seeSpecification).

The mixture of cement, sand, and aggregate is prepared in the proportion 1: 2: 4, and clean wateris added, cautiously to avoid making it too wet. The total volume of concrete needed for eachcaisson mould as described in the shop drawings, is 136 litres. Allowing 10% for losses, thisvolume can be conveniently mixed with a single 50 kg bag of cement. A corresponding gagebox for the measurement of sand and aggregate, would be a 33 litre box, or a box with internaldimensions of 32 cm x 32 cm x 32 cm.

The concrete should be added equally all the way around the mould, in order to preventdistortion. It should be rodded as it is added, carefully in order to avoid damaging the base plate.The mould should be tapped with a soft mallet in order to vibrate the concrete into all cornersand spaces in the mould.

The caissons should be kept moist for the first week after casting, or until used in the well, bysprinkling with water several times daily and by covering with wet cement bags.

6.3 Cutting RingsWhen caissons with rebate edges are correctly orientated, there is usually little or no need for acutting ring. Nevertheless, cutting rings may be found useful in certain soil conditions. Thecaisson moulds described in this document can be used to produce cutting rings when needed.This is accomplished by adding 47mm thick wooden blocks in each of the joints of the outermould to increase its diameter by 30mm. This allows the outer mould to be mounted outside thebase plate, and the capping ring to be mounted inside the outer mould. This in turn creates acutting ring of 3 cm greater diameter, or 1.5 cm greater radius than the caisson rings.

6.4 Excavation

6.4.1 Caisson Lining MethodsThere are two methods for lining a well with caissons. One is the “Dig First Line Later” method,which is similar to the In-Situ casting method, except that finished caissons are lowered downthe hole in place of shutter moulds. The second and perhaps more important method is the“Caisson Sinking” method.

It is common to use both methods in one well, digging the unlined hole to a comfortable depth instable soils, then lining that section with caissons and proceeding to sink them in order to deepenthe well to greater depths and in unstable soils. What is most important is that the workersshould be familiar and comfortable with the Caisson Sinking method in order that they shouldnot postpone placing the caissons in the hole until it is too late.

6.4.2 Moving and lowering caissonsImproperly handled, the moving and lowering of caissons are two of the riskiest components inthe well digging process. Done correctly and with adequate preparation, there is very little riskinvolved. In the first place the tasks should be undertaken with the essential number of workers,


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not more, and especially without crowding. It is not uncommon for spectators to rush to helpwhen the caissons are to be moved. They should be warned to stay back.

Tipping caissons on edge

The caisson can be tipped safely by three or four workers. If it is resting on a hard surface asmall lever and spacers may be needed to make space for the workers’ fingers. On a soft surfacethey can usually get their fingers under the edge. Small blocks of wood should be placed nearbyto prevent rolling once the caisson is raised, especially on sloping ground. The caisson is raisedby main force until the balance point, then held back so that it settles slowly onto its edge. Thisshould be accomplished in one smooth action without pausing at the balance point. If thecaisson is to be left on edge then blocks should be placed to prevent rolling. Workers, spectators,and especially children should be warned to stay off them.

Rolling the caissons

Caissons can be rolled by two to three people in most instances. If they must be moved up ordown slopes then additional workers may be used judiciously, provided that crowding isavoided. One or two workers can be stationed ready to insert blocks to prevent rolling when theothers are resting.

To roll up steeper slopes, a rope can be tied off at the top of the slope, placed under the ring, anddrawn back over the top. Several workers can then pull from above while four workers steerfrom the sides, and one is stationed with a block to insert in case of need. This operation must beplanned and laid out carefully so that the rope is laid straight up the centre of the path of thecaisson. The caisson itself must be carefully steered to stay centred on top of the rope.

A similar method can be used to descend steeper slopes, but here the planning must be all themore careful. The rope can not be safely placed once the caisson is on the slope. It must bedone before. The rope handlers must keep the rope centred above the caisson as it descends.There must be adequate length of rope to enable the caisson to reach the bottom of the slopewithout crowding the workers. It is very important that the route of the caisson be planned indetail, including where it would end up in case of mishap. If a safe direct route can not be found,then consider taking a round about route to avoid the steep slope.

Tipping the caisson over the well

Settling the caisson over the well can be extremely dangerous if proper preparations are notmade in advance. When the method is known and preparations are made, there is very little risk.In the first place, no worker should be in the well when this work is being done!

A simple temporary support structure is placed over the well to receive the caisson. A side railof the head frame can be used as a part of this structure if the caisson is to be lowered through it.The head frame is slid along sufficiently to allow clear access to the well. If the head frame isnot in place, then a single pole about 3 metres in length should be placed over the near edge ofthe well in roughly the position that the near rail of the head frame would be. Now a second poleof similar length is placed across the well resting on top of the first pole or the head frame as thecase may be. The cross pole should have ample overhang above the soil on each side of the well.The thickness and weight of the poles will depend on the strength of the local woods. Ten-cm byten-cm square cross section will be adequate if strong hardwood timber is used.


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Now the caisson is rolled into position beside the well with the lower edge facing towards thewell and the near rail of the temporary support. It is manoeuvred into a position such that itsnear lower edge is about 50 cm (in the case of 110 cm OD rings) away from the top edge of thenear rail.

The caisson is tipped slowly towards thewell, and lowered as slowly as possibleonto the temporary support. In this, theadditional height of the head frame is aconsiderable advantage, as the caissonhas less distance to fall. In the casewhere sufficient height is not achievedby the temporary support to lower thecaisson slowly into place, the cross polemay be raised by one or two workers onthe other side of the well to meet thecaisson, preventing it from falling ontothe support. In this case the workersmust exercise caution to avoid shiftingthe support structure out of its finalposition, and to avoid sliding the crosspole into a precarious position.

The resulting position of the caisson is near horizontal, with about one half of its diameterprojecting over the edge of the well. This is sufficiently close to lift it without risk of tipping thetripod over.

Lifting and lowering caissons

It will be noticed that very little lowering of caissons is necessary when caisson sinking is usedfrom the surface down. When the in-situ casting method is used, a deep hole may be preparedbefore the first caisson is lowered in. What is more, in this instance all of the caissons must belowered almost the same distance.

A tripod and winch are used for lifting and lowering caissons. There are various methods forattaching the winch to the caissons: Ropes wrapped around the bottom of the caisson should beavoided for several reasons: The caissons supported by ropes under them are inherently unstable,and hang crooked. Once removed, it is very difficult to reattach the ropes in order to manoeuvrethe caissons down the well if needed. The wear and tear on the ropes is very costly.

In this document we describe a caisson design with two lifting holes placed above the centre line,and a lifting bar which is inserted in these holes. This apparatus can be manufactured at littlecost in most competent machine and welding shops. It is more secure and exerts less stress onthe caisson itself than is the case with lifting callipers.

The tripod, winch, and lifting bar should all be inspected each time they are used to ensure safeoperation. The winch cable must be wound carefully and smoothly on its spool to achieve longlife and safe operation. The tripod should be firmly based, with its legs equally spaced and itsfeet at equal elevation. Ideally the legs of the tripod should be inclined at about 60 degrees fromthe horizontal. The top of the tripod should be centred over the well. With careful placement, it


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should be possible to operate the tripod over top of the head frame, without interference, onewith the other.

In the event that it must be moved, it is useful to mark the position of each foot so that it can bereturned to the same spot each time. It is possible to move the tripod short distances by walkingthe legs short distances, one at a time. Moving more than one leg at a time is very dangerous. Inany event the roughly equal placement of the legs should be maintained for stability.

Caissons must never be lowered into the well with a worker below! The winch is attached to thelifting bar, and the cable is tightened to carefully lift the caisson off the temporary support. Arope may be attached to prevent an uncontrolled slide toward the centre as the caisson is lifted.

The worker operating the winch must be familiar and prepared to use its braking capabilityduring lowering. In some instances two workers may operate the winch as a team. Maintainingcontrol of the winch handle during lowering is of paramount importance. Once control is lost, itis unlikely to be regained, as the handle may spin at dangerous speeds, and can not be caughtwithout injury to the worker.

If the lowering depth exceeds the safe operating length of the winch cable, then the caisson mustbe suspended part way down while an extension is added to the cable. For this purpose, chainsare the most convenient. It should be noted that not one, but two chains are needed, one tosuspend the caisson, and the other to extend the cable. This is mentioned because the greatestprobability of accident and injury results from makeshift methods of extending the cable orsuspending the caisson.

6.4.3 Placing and levelling the caissonsIf some excavation has been completed before the first caissons are added to the well, then it isimportant to prepare the existing shaft. It must be large enough for the caissons to be lowered,vertical enough to avoid tilting the column of caissons (although final trimming can be made asthe caissons are placed if necessary), and levelled at the bottom to provide the caissons with asuitable temporary base.

It is not advisable to join the caissons together with mortar until one is fairly confident that thefinal rings are being installed. The top three metres of caissons in the finished well should bejoined with mortar in order to seal out potentially contaminated surface water. It may bepossible to estimate which caissons will be in the final three metres after the water table has beenreached, but not before.

Before caisson sinking begins, the existing column of caissons should be well fitted, vertical, andfastened together. Careful undercutting to level the bottom caisson, and trimming of the sidewalls as necessary to allow the stack to stand vertically, should enable to workers to achieve avertical and well fitted column fairly easily.


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6.4.4 Attaching caissons togetherOne of the greatest challenges incaisson sinking is to prevent thebottom ring in the stack from fallingout of line. In order to sink thecaissons, they must be undercut.Without suitable precautions, one sideof the bottom ring can fall ahead ofthe other. When this happens, thatside tends to fall inwards. When theother side is induced to come down, ittends to move outwards so that thecaissons are no longer aligned. Afterthis happens it is very difficult tocorrect the situation or to prevent itfrom worsening. There is, however, asimple and effective method toprevent the problem.

During caisson sinking the bottom three to six caissons are temporarily bound together with steelrods. Various methods are available to attach the rods to the caissons. In this document wedescribe attaching the rods to pins placed in the same holes used for lifting the caissons, as thismethod leaves the bottom edge of the bottom ring free and does not interfere with digging. Thebinding rods also provide a convenient place to hook tools out of the way when they are not inuse.

It is recommended that the binding rods be attached as soon as there are more than two caissonsto join together. When problems develop it is already too late. In the event that one side of thebottom caisson separates before the rods are in place, the excavation should be stopped while theattempt is made to lift the bottom ring back into place and attach it.

6.4.5 Digging and caisson sinkingAs is the case in any trade, including other aspects and methods of well digging, caisson sinkingcan be taught in one or two weeks of training, preferably in two or more sessions. The learningcurve, however, will endure for years. The diggers develop a feel for their trade, which includesan intuitive understanding of the best methods to undercut a caisson in soft or unstableconditions, hard soil conditions, rocky conditions, etc, which will be refined over a period ofyears.

At a more elementary level, it is necessary to begin with the correct tools and suitable designs.One of the pitfalls of the last decade and a half of well digging projects has been that engineersand project managers have provided shovels and pickaxes for excavation in an environmentwhere they simply can not be used. Digging in the more confined space of a caisson ring isvirtually impossible if the only tool available to fill the bucket is a shovel. Undercutting isextremely difficult if caissons with rebate edges are inserted the wrong way up, if caissons aretoo thick, or if a cutting ring of poor design is used.


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Tools for caisson sinking

While a more complete equipment list is presented in Appendix 1, it may be useful here toclarify what tools are appropriate for digging in confined spaces. Several conventional andmodified tools are useful items forcaisson sinking.

There is one essential, however,without which the job becomes nearimpossible. A short digging hoe isprobably the most important tool fordigging and filling buckets. A shovelwill not accomplish these purposes.The digging hoe is a broad hoe with ahead approximately 20 cm x 20 cm. InIndia it is called a “powerah”; in WestAfrica, simply a hoe (although thisdescribes several local diggingimplements, some of which are verysuitable, and some of which are toolight for the purpose). The handleshould be about 55 - 60 cm long. Thedigging hoe is used for soft digging,collecting and scooping up loosenedsoil, and loading the bucket.

A second essential tool is the pick. If itis unavailable in its simple form, it isuseful to modify the pickaxe that isalmost universally available by cutting off its pointed tine and shortening the handle to 55 - 60cm. If a pointed tine is desired for excavating in very hard soil or soft rock, then a secondpickaxe can be modified by cutting off the flat tine.

A digging bar, commonly called a mine bar or crow bar is sometimes useful for excavating inhard soil, but shortened to about 90 cm, it will be useful for loosening stones in the confinedspace of the caisson ring.

A spirit or water level, about 60 cm long is needed to ensurethat the caissons are sinking level, especially at the start of thesinking process. When the column of caissons becomes muchlonger, a plumb bob will serve the same purpose.

Digging in confined spaces

There is nothing particularly difficult about digging in theconfined space of a caisson ring, once the correct tools arechosen. While the soil is loosened with a pick, the bucket canbe pulled up above the worker’s head, and the digging hoe canbe hooked behind one of the binding rods where it is out of theway. When it is time to load the bucket, the pick can be


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hooked behind the binding rods, while the bucket is tucked between the digger’s legs. It is asimple matter to scoop up the soil and drop it in the bucket. Once again, it is the choice of toolsthat makes all the difference.

Elementary caisson sinking

With experience, diggers will find that caisson sinking is not significantly more difficult thandigging an unlined hole. In many ways it is easier, owing to the smaller volume of earth to beexcavated, and to the elimination of a centring and truing cut and the lining phase which arerequired in other methods of well lining.

When the first caisson is placed in the hole it is important to centre and level it. Periodicchecking of the level, especially as the first few caissons are added, will save much difficultylater on.

The sinking begins with excavation of a small hole at thecentre of the well. This hole is then expanded outwardsuntil the inner edge of the caisson is reached. The mostcomfortable shape of the bottom of the hole duringundercutting will depend slightly on the type of soilbeing excavated. In soft or unstable soil, it will be usefulto keep the bottom profile very flat, while in very hardsoil it is worthwhile to advance a bit more at the centrebefore undercutting. Useful methods for a variety of soilconditions are discussed in the following sections.

When a comfortable bottom profile is achieved, it is time to start undercutting. This is usuallydone with the flat pick. It is useful to undercut about 7 to 10 cm at a time, unless unstable flowsof sand or silt have been encountered, in which case the undercut is reduced to 5 cm or less. Theunder cut is balanced on all sides of the well, and continuously expanded until the caisson sinksdown.

The centre cut, excavation to a suitable bottom profile, and undercutting are then repeated untilmost of the first ring is submerged in the new hole. The level should be carefully checked andcorrected before the second ring is added.

When the second caisson is added, it is useful to add one or two more at the same time, andattach them together with the binding rods. This will ensure that the stack moves together andthat the first ring does not get out of line. The level should be used periodically during thesinking of this initial stack to ensure that the initial hole is plumb. As digging proceeds, the holeitself will help to keep the stack aligned and plumb.

Experience shows that slightly different digging strategies are needed depending on the soilconditions at the bottom of the well. As different strata are reached the diggers will have torecognise the changes and adapt their techniques to suit. The following sections provide someinitial hints for the various conditions.

Soft soil conditions

As was mentioned in our initial discussion of the basics of caisson sinking, the bottom profilewill be slightly different depending on the soil conditions. In the case of soft soil, it is not


30

advisable to advance too far below the leading edge of the caisson ring. A suitably controlledsubsidence of the ring may be achieved with the bottom dished about 15 to 20 cm below theleading edge. In very soft soil, it may be necessary to reduce this to only about 10 cm, or evenless in the case of flowing sand, silt, and mud. See the section on stopping sand, silt, andmudflows below.

Hard soil conditions

In hard soil conditions it is permissible to advance the centre of the hole somewhat farther aheadof the leading edge. In this case it is all the more important that the bottom three to six caissonsin the column are securely fastened with the binding rods, and that the undercutting is restrictedto a section not exceeding 5 - 10 cm deep immediately below the leading edge of the caissonring. Again, in the case of flowing sand, silt and mud, The dishing of the bottom should belimited in an effort to have the leading edge cut through the flow and cut it off. See the sectionon stopping flows below.

Rocky conditions

In rocky soil, a great variety of conditions might prevail. Consolidated layers of rock, oroccasional boulders of various sizes.

(i) Consolidated rocky strata

In the case where a consolidated layer of progressively harder rock is encountered, the decisionmight be taken to carve a level seat in the top of the rock on which to rest the bottom caisson.The workers may then proceed to hollow out the rock at the inner diameter of the caissons. Thisforms a natural lining, and the prognosis for success or failure of the well is best determinedfrom local experience. It is possible that a small source of water will have been encountered justabove the rock, and that all that is required is a small reservoir excavated in the rock to takeadvantage of this source. On the other hand, local experience may show that fractures orchanges of strata may be encountered at not too great a depth, and thus the excavation proceedsin search of sources of water at greater depths. This work progresses from pick work to hammerand chisel work as the rock becomes harder. Provision of a hammer and chisels of sufficientquality may allow a substantial water source to be carved from the rock. It is found that in manycases the local experience consists of constructing small reservoirs in the top of a consolidatedrock layer. In such cases the provision of suitable hammers and chisels may make the differencebetween a minuscule source that must be dipped by hand, and a substantial reservoir capable ofserving several families with improved methods of accessing the water.

(i) Isolated rocks or boulders

Where isolated rocks are encountered during excavation, they must be freed from the soil aroundthem and pulled out of the well. In many cases they can be simply put in the bucket and hauledup. In other instances they must be attached to the rope from the windlass or even the winchcable. In the latter case, of course, the workers must attach the rope and leave the well before therock is lifted.

Rocks of significant size can be encountered in many different ways during caisson sinking.When found in the centre of the well they present relatively little problem, except in the amountof labour required to break them free from the surrounding soil. Often they will be encountered


31

under the edge of the caisson ring, in which case it is important to remove the rock into the wellbefore undercutting the rest of the circumference of the caisson. Usually it is possible toundercut enough to tip the rock into the well.

When rocks are encountered outside the wall of the caisson, a crucial decision must be made todetermine whether the caissons can safely pass by. If there is any doubt at all, then the rockshould be undercut and removed into the well. Sinking the caissons further might make this taskmuch more difficult. Often the size of the rock can be approximately determined by diggingaround its upper parts. The removal, however, can only be accomplished by thoroughundercutting, and sometimes, even excavation behind the stone.

In the case of boulders too heavy to lift out with the winch, or too large to remove through thewell, it is occasionally possible to break off enough of the boulder to allow the rings to passfreely. It should be noted that blasting with the boulder in direct contact with the caisson ring islikely to break the ring as well.

In the event that the boulder is centred in the well, or for other reasons can not be removed, itmay be necessary to abandon the well and start again a short distance away. In this case it isusually possible to salvage most of the caisson rings. Obviously in the case of in-situ casting, thewell lining must be abandoned.

Stopping sand, silt, and mud flows

One of the greatest advantages of caisson sinking is that it is possible to excavate through a mudor sand flow and cut it off so that the well construction can continue. It is important to stop suchflows, both in order to achieve a clean and maintainable well, and to avoid contaminationthrough sub-surface funnels. Of greater immediate importance, is that if there is a section of in-situ casting above the flow, then the cavity created by the flow can cause the anchors of thelining to be undercut, and the lining to subside or fall right into the well.

There are a variety of techniques that can be tried in order to more effectively cut off the flow ofliquid mud or dry sand or silt into the well. First and foremost is to attempt to settle the rings asmuch as possible by undercutting all sides in addition to the portion where the flow is entering.The dishing of the bottom should be reduced and the vertical depth of the undercutting should beminimised, especially on the side towards the source of the flow.

If this method fails, a decision may be taken to allow some of the material to accumulate in thewell. Stopping the excavation for up to several hours, or overnight, may allow the solids in theflow to settle out and stabilise, once the flow is slowed down by the back pressure ofaccumulated material within the well. Dewatering should be stopped during the pause, as theback pressure of the accumulated water will also help to slow the flow and allow the solids toconsolidate.

If the flow can be seen from above, around the outside of the caissons, it may be possible to slowit sufficiently by pouring course dry sand down into the portion where the flow sinks along theside of the caisson. Occasionally pushing brush foliage into the flow can also be effective. Itshould be noted, however, that this foliage is difficult to remove after the flow is stopped. If leftin place, it will decompose behind the wall of the caisson, and may cause an unpleasant taste andodour to the water for many months after the well is completed.

Persevere. If one of these methods does not work, proceed to the next, and attempt themrepeatedly.


32

6.5 Dewatering During ConstructionOne of the main objectives of an improved dug well, is a substantial water source of a qualitysuitable for pumping, and dependable during particularly dry years. In order to achieve theseconditions, it is necessary to continue excavating and caisson sinking, typically 2 - 3 metresbelow the water table. In some areas where the water table is known to fluctuate more than this,even more depth is required. As the deepening proceeds, it is necessary to remove more andmore water along with the soil. At the beginning the lifting head frame and bucket may besufficient to achieve this purpose. As the work progresses, however, a point is reached whereexcavation can not continue without mechanical means of dewatering. There are severalpossible methods of dewatering, and they are not all equally safe or equally effective.

6.5.1 Engine driven centrifugal pumpsIn the case of very shallow wells, a simple, gasoline driven centrifugal pump may be used. Thisshould be one of open impeller design to allow some solids to pass. It should be self-priming oreasy to prime. It should have sufficient intake hose to permit the pump to be placed back fromthe well, down wind, and preferably behind a shallow dike to prevent the exhaust fumes fromentering the well.

A centrifugal pump has some serious disadvantages. It is usually difficult to throttle downsufficiently, and so must be shut off when the well runs dry. It is inconvenient to start and prime,and gets progressively more difficult as the depth increases until a point, typically around 7metres depth, where they can not function. There will be a temptation to move the pump closerto the well or even to lower it into the well. This must not be permitted, as the exhaust fumes areone of the most serious dangers encountered in well digging.

6.5.2 Electric submersible pumpsElectric submersible pumps are available in a great variety of qualities. They may be used indewatering, if suitable attention is given to protecting the electric cord, and to grounding thegenerator to avoid shock hazard at the bottom of the well. A submersible sump pump or minedewatering pump design is suitable because of the open impeller design and the built inexclusion screen to prevent too large particles from fouling the impellers. Sufficient pumpinghead must be available at the anticipated flow rates. Size is also a concern, as too great a sizewill interfere with the digging operations.

Reliance on external float switches can be awkward in the confined space of the well. If a builtin float switch is removed or broken, then the wire ends must be very thoroughly sealed andtaped out of harm’s way.

Generators purchased to operate a submersible pump should be selected for the necessary powerconditions, but also of portable design. It is important that sufficient cord be provided to allowthe generator to be installed well back from the edge of the well, down wind, and preferably overan embankment of soil. The cord should be of sufficient capacity to accommodate the extralength, and of industrial quality insulation for safety. Worn extension cords must be replacedregularly


33

6.5.3 Compressor driven pumpsCompressor driven pumps are available in both centrifugal and diaphragm types.

The centrifugal design tends to be extremely hardy against external shocks, dirty water, etc.Their capacity is usually too high for the dewatering purpose and they are not easy to throttledown for slower continuous operation.

Diaphragm type pumps are available in a variety of sizes. They can be more successfullythrottled down for continuous operation. Nevertheless, excess size should be avoided in order toallow room for the digging to continue during pumping. These pumps should be fitted with anintake structure with screen near the bottom, to avoid blockage. The diaphragm design issometimes sensitive to levelling, and operates less efficiently when sloped to one side or theother.

Compressor driven pumps have air motors that are sensitive to dirt in the air provided. Air hosesshould be kept clean, and the ends capped when not connected to the compressor and pump.

Compressors should be selected with sufficient pressure and volume capacity to operate theimplements selected. It may be more difficult, however, to identify compressors with lowenough capacity for capital and fuel savings, as well as portability to the well site.

Compressors should be supplied with sufficient air hose to allow them to operate well back fromthe work site, preferably down wind and beyond an earth embankment.

6.6 Finishing the Intake SectionCaisson sinking should continue until the well has achieved sufficient depth of water andsufficient flow. These conditions should be estimated in the late dry season to ensure that thereis still sufficient capacity and depth. Typically this should be specified as a minimum 2 - 3metres of water depth, and 10 to 20 litres per minute of recharge. (i.e. Minimum standards maybe set at 3 metres with 10 litres per minute, 2.5 metres with 15, or 2 metres with 20 litres perminute.)

Initial fill and levelling the bottom

Once the final depth has been reached, an effort should be made to ensure that the bottomcaisson is well seated all around. It is good practise, then to level the bottom and clean outremaining loose mud and silt. Before this operation is undertaken, it is useful to add a fewbuckets full of the clean gravel intended to backfill the water-bearing zone of the well. This willallow some of the aggregate to migrate down into any soft mud, sand, or silt flows in the water-bearing zone. The gravel fill should not be overdone, and should not rise far above the water-bearing zone. See the section on initial backfill below.

Bottom plugs

Bottom plugs serve very little practical purpose in the functioning of the well. Engineers haveoccasionally proposed that they would help to prevent materials from rising from the aquifersinto the wells. There are few cases where this is desirable. Any material in the aquifer that ismobile enough to rise in the well should be allowed to do so. It is much more likely to harm thewell if it is blocked in some manner.

One purpose that bottom plugs do achieve is to facilitate occasional cleaning of the well. Ten


34

centimetres of clean gravel make a suitable separation with which to identify the limits of thewell during occasional cleaning. Concrete plugs should be discouraged as unnecessarily costlyand complex.

Initial backfill

The initial backfill completes the intake section. It consists of fine gravel or other permeableaggregate, in the water-bearing zone. It is often not possible to add much aggregate to the verybottom sections, as sand or mudflows may already have sealed off that portion of the well. Thefinal seating (sinking) of the caissons may help the gravel to migrate into these flows duringcompletion of the intake section. Some gravel can generally be added, at least to the top of thewater-bearing zone. It should not be overdone, and in any event should not approach the sealedsection in the top 3 metres of lining.

In the case of caissons used to complete an in-situ cast well, the gravel filter can be filled in up toabout 15 cm below the top of the top caisson, and above the level of the bottom edge of the in-situ casting. The final 5 cm may then be filled with a weak concrete plug achieved by a 1:5:8mixture of cement, sand, and gravel.

In the case of caisson lining to the surface, clean soil selected from the material taken from thewell can be used as backfill above the water table. More permeable materials can be used nearthe bottom section, and impermeable materials near the top.

6.7 Sealing the Upper ShaftWhile avoidance of surface water does not guarantee safe drinking water, it helps a great deal. Itis normal practise to seal the top 3 metres of well liner, and to exercise caution in the top sectionof the back filling and drainage to prevent short-circuiting of the surface water to the unsealedsection below.

Evidently, in the case of in-situ casting, the top section is automatically sealed, provided that theupper 3 metres were cast in one lift, and with sufficient care taken to achieve a bond betweencourses of concrete.

In the case of caisson lining in the upper sections, this seal is not automatically achieved, andmust be placed manually. This can be done in several possible ways:

Surface plastering over the joints between caissons can be used, forcing as much plaster aspossible into the joint and then smoothing over the surface around the joint.

It is sometimes easier to anticipate the need to seal the top caissons before the final excavation isreached and to place a weak mortar in the joints as the caissons are added. If the need is notanticipated, the upper caisson rings can be lifted again to place a cement sand mix in the joints.

Where the above methods are used to seal the caissons, the upper portion of the shaft can be backfilled with impermeable soils, mounding the soil above the surface somewhat to encouragedrainage away from the well.

An alternate method of sealing the top portion of the shaft is to pour a weak concrete mix in thespace around the caissons. This method can only be used where the gap is narrow, resultingfrom careful excavation or caisson sinking from the surface. If subsidence or caving has causedlarge gaps around the caissons near the surface, then these caissons should be sealed by thepreviously mentioned methods, and the remaining holes filled with impermeable soils mounded


35

above the surface some 10 cm to cause drainage away from the well.

6.8 Construction of the Head WallIn the case of caissoning to the surface, the head wall can be constructed by simply addingadditional caisson rings and partial rings until the desired height is reached. These rings can becemented in place with a weak cement sand mix.

In the case of in-situ lining, the head wall can also be cast in-situ with the addition of an outermould for the aboveground section.

The head wall height will be determined either by standardised designs, or by the decision to usea hand pump, hose and bucket pump, windlass, etc. SeeStructural Drawings

6.9 Construction of the Apron and DrainageA suitable apron and drainage are essential parts of any improved well. The requirements mayvary considerably depending on the pumping methods and purpose the well is to be used for.

If a mechanical pump is to be fitted, it may be sufficient to mound the soil around the head wall,and to add a cast top with a manhole cover for maintenance access.

If people are to go to the well to fetch water, a concrete apron or platform around the head walland sloping away from the well is essential. A raised edge on the outer rim of this apron collectsthe water and channels it to a lined drainage channel that carries the water away from the well.SeeStructural Drawings

The most important consideration in construction of the apron and drainage is to determine onwhich side of the well the natural drainage would run. i.e. Which is the lower side? If it is foundthat water would not naturally drain away from the well, it is necessary to provide additionalearth fill, using the earth accumulated in the excavation of the well. This soil can be built uparound the wellhead to raise the apron to an elevation that can be drained away from the well.The soil mound can be shaped roughly to the same slope intended for the eventual apron. Thiswill conserve concrete in casting the apron, and also ensures that there exists a seal and a slopeaway from the well, even under the apron.

One final detail is that the apron is likely to resist cracking from uneven settling better if theconcrete is not poured directly against the head wall. A layer of clay plastered on the headwallbefore the apron is cast can help to maintain a flexible joint. The top of this soil plug can later bescraped out and replaced with a seal of tar or bitumen.

6.10 DisinfectionWhen the well is new, or after workers have entered the well for maintenance and cleaningpurposes, it is advisable to disinfect it. This is done by scrubbing the inside surfaces that mighthave been exposed to contamination with a mild chlorine bleach solution, and by treating thewater in the well with sufficient chlorine to achieve 5 ppm free chorine in the known volume ofwater. While this concentration is only about one sixth of that recommended by manyprofessionals, it is also seven times the level recommended for water treatment, and willsuccessfully disinfect any surface contamination that water is in contact with.

The practise known as shot chlorination, raising the chlorine concentration to highly toxic levels,


36

and periodic chlorination of the well are to be discouraged. Raising the chlorine concentration totoxic levels disrupts the natural environment of the well and aquifer, without achievingsignificantly more decontamination than is achieved by chlorinating within the potableconcentration range. Periodic chlorination, again, disrupts the natural environment of the wellwithout providing any protection beyond the hour or two in which the chlorine remains in thewell.

In the event that the well is known to be contaminated or small organisms are found in the water,the source of the contamination should be found and corrected before decontamination. Simplykilling off the existent organisms with chlorine compounds produces an offensive taste andodour, resulting from unnatural decomposition processes, without preventing re-contaminationfrom the original source.


Appendices

37

Appendix A Equipment List for Hand Dug Well ConstructionThe following list of equipment is intended for the guidance of those setting up a regional welldigging program for the construction of approximately 100 wells per year, through hiring ofmultiple contractors.

The number of each item desirable is estimated by region, by contractor, or by well site,depending on the normal deployment of the equipment. An asterisk (*) following the numberindicates that item should be regarded as essential, and mandatory for the contractor to qualifyfor a contract.

Description No. Unit

Reqd.Per

Class Comments

Safety Equipment

1 Helmet (Climbers’ model) 2 * Site Minor Import if unavailable

2 Rescue harness 2 * set Site Minor Import webbing ifunavailable

3 Locking Carabiner 4 * Site Minor Import if unavailable

4 Rope ladder oralternative

1 * Site Minor Quality controlled local

5 Goggles 2 pair Site Minor Essential with power tools

6 Ear Protection 2 pair Site Minor Essential with power tools

7 Work gloves 2 pair Site Minor Depending on Culture

8 Wellington (rubber)boots 2 pair Site Minor Depending on Culture

Light lifting head frame * See Lifting Equipment

9First Aid Kit

1 * Site Comprised of thefollowing:

Adhesive Bandages 25*

Site

Adhesive Tape 1 * roll Site

Sterile Gauze Compress 10*

Site

Gauze bandages 5 * roll Site

Triangular bandage 2 * Site

Hand soap 1 * Site


Appendices

38


Reqd.Per

Class Comments

Scissors 1 * Site

Tweezers (forceps) 1 * Site

Measuring Tools10 Spirit level 1 * Site Minor

11 Plumb bob 1 * Site Minor

12 Plumbing String 100*

feet Site Minor

13 Tape measure, 16 ft. (5m)

1 * Site Minor

14 Tape measure, 100 ft.(30m)

1 Site Minor Optional

Additional MeasuringTools for In-Situ LinedWells

15 Plumbing Rod 1 Site Minor

16 Trimming Rods 1 pair Site Minor

Digging EquipmentSketch of Digging Tools

17 16mm Rope 100*

feet Site Minor

18 Bucket (heavy dutyhandle)

3 * Site Minor

19 Digging hoe 2 * Site Minor Either Local or Import*

20 Pick, flat blade 2 * Site Minor Modified Pickaxe*

21 Pick, pointed 2 Site Minor Modified Pickaxe*Optional

22 Mattock 1 Site Minor Optional


Appendices

39


Reqd.Per

Class Comments

23 Miners’ bar (90 cm) 1 * Site Minor Large bar modified bysmith

24 Masons’ hammer (4 lb) 1 * Site Minor

25 Cold chisel, flat blade 1 * Site Minor

26 Cold chisel, pointed 1 Site Minor Optional

27 Wheel barrow 1 Site Minor Optional

Additional DiggingEquipment For In-SituLined Wells

28 Moore (sledge) hammer 1 Site Minor Optional

29 Spade (short handle) 1 Site Minor Optional

Lifting, BindingEquipment Sketch of Major

Components

30 Light lifting head frame 1 * Site Int Local Manufacture

31 Tripod &

Winch

1 *

1 *

Site Int Local manufacture

Import M&F ast orequivalent

32 Caisson lifting bar 1 * Site Local manufacture

33 Caisson binding rods 1 * set Site Local manufacture

Concrete Mixing &Casting

34 Shovel 2 * Site Minor

35 Masons’ trowel 2 * Site Minor

36 Float 1 * Site Minor

37 Wire brush 1 * Site Minor

38 Rubber mallet (1 - 2 lb) 1 * Site Minor For tapping forms


Appendices

40


Reqd.Per

Class Comments

39 Head pans 2 * Site Minor

40 Guage box 1 * Site Minor

41 Water barrel orequivalent

1 * Site Minor

42 Sieves 1 set Contr. Minor Optional

43 Cement mixer or mixingpad

1 Site Int Recommended

Miscellaneous44 Hacksaw and spare

blades1 * Site Minor

45 Pliers 1 * pair Site Minor

46 Spanners (combinationwrenches)

1 * set Site Minor To fit all mould, headframe, and tripod bolts

47 Vicegrips 1 * Site Minor Recommend Peterson10WR

Caisson Moulds

48 Caisson ring mould 2 * set Site Int Manu.& Financial assist.

49 Base plate / Rebatemould

6 * Site Int Local manufacture

50 Capping Ring / Rebatemould

2 * Site Int Local manufacture

51 Moulds to form baseplate and capping ring

1 pair Optional

Additional Moulds forIn-Situ Lined Wells

52 Lining mould, inner 4 Site Int

53 Lining mould, outer 2 Contr. Int


Appendices

41


Reqd.Per

Class Comments

54Well Head Moulds

1 set Contr. Int Optional, Comprised of:

Apron form 1 Optional

Pump base mould 1 Optional

Inspection hatch basemould

1 Optional

Inspection hatch covermould

1 Optional

Insp. hatch extensionmould

1 Optional

Carpentry Tools55 Carpenters’ hammer 1 Site Minor

56 Try square 1 Site Minor

57 Hand saw 1 Site Minor

58 Pry bar (Crowbar) 1 Site Minor

59 Carpenters’ chisel 1 set Site Minor

60 Plane 1 Site Minor

Dewatering, Breaking,etc

61 Compressor or generatordewatering, breaking,drilling set (small)

1 Set Contr. Int Electric generator withdewatering pump,breaker, and hammer drill

All components must beselected with extremecare to match generatorcapacity with pump andtool requirements.Suppliers should beasked to demonstratecompatibility ofcomponents beforedelivery.


Appendices

42


Reqd.Per

Class Comments

62 Compressor dewatering,breaking, drilling set (big)

5 Set Regio. Major Atlas Copco XAS 32-36compressor with ARO 1"non-metalic diaphragmpump, Atlas Copco TEX14PS and TEX 18PSbreakers, and AtlasCopco BBD 12T-01 rockdrills

Substitutions should bemade with considerationfor size and airrequirements of eachcomponent.

For purposes of calculation, we would suggest that the number of active digging sites may beestimated as approximately 0.25 to 0.33 of the total number of sites that the contractor isexpected to complete in the whole digging season.


Appendices

43

Appendix B Specification for Hand Dug WellsBelow are modified specifications extracted from a Ghana CWSD bidding document.Modifications have been made to permit the following initiatives:

� To permit optimisation of caisson designs with smaller wall thicknesses, and to permitthe use of caissons above the water table, whether in stable or unstable conditions.

� To introduce more specific standards for testing of yields� To allow for variation of slope to achieve drainage to one single outlet. Apron slope

has been reduced to 2 - 5% from the original fixed 5%.� Apron overall dimensions have not been changed although 4.75 m square or diameter

appears excessive. Such standards should be established on a project by project basis.� To revise the old standard requiring that concrete be used within two hours after being

mixed. The corrected standard reads “within 30 minutes”

1. Site selection1.1 Site selection will be made by the community with the assistance and support of the

regional rural water supply engineer and the zonal hydrogeologist. Where geophysicalconditions in an area are particularly favourable, well siting will be based on observationof local geologic conditions and existing water wells. If there is uncertainty that a dugwell can be successfully constructed, a small diameter test hole may be bored; and if atest hole can not be constructed, and the likelihood of constructing a successful well isbelow about 75%, a geophysical survey will be conducted.

2. Site Preparation2.1 The community shall clear and roughly level a minimum working radius of 12m

measured from the centre of the proposed well. Such clearing, however, should notconsist of tree cutting except as absolutely necessary. The community shall also provideshelter to store cement and hand tools.

3. Excavation3.1 The excavation of the well shall be to the dimension specified in the drawings.

3.2 The centre line or axis of excavation must be vertical to within 10mm per meter of depthof the well.

3.3 Unless soil conditions allow otherwise the first lift should be excavated to a depth of notmore than 5.0 meters before the start of in-situ lining with concrete or precast caisson


Appendices

44

lining. The final trimming of the walls shall be done not more than 24 hours before thecasting of in-situ concrete lining. The finished diameter of excavation shall be asspecified in the drawings. ie. 1.5 metres dia for in-situ lined shaft, and 1.1 metresdiameter for caisson lined shaft, and shall be maintained constant about the axis.

3.4 Excavated material shall be placed at least 4 meters away from the edge of the excavationin order not to interfere with construction. Excess excavated materials will be disposedof by individual communities as agreed in their Facilities and Management Plans.

3.5 If rock is encountered during excavation, the contractor must give notice in writing to theProject Manager that he has encountered rock and that he intends to claim payment. Hemust state the equipment he intends to use. Rock is defined as solid material which canbe removed by chisel and hammer, blasting, or use of pneumatic tools and includes onlyboulders larger than 0.5 metres diameter.

4. Lining

In-situ lining4.1 In-situ lining shall have a minimum thickness of 100mm and a finished inside diameter

of 1.3m. It shall be cast in-situ from concrete having a 1:2½:5 mix if cement, sand, andaggregates.

4.2 The shuttering shall have a maximum deflection from vertical of 10mm per meter height.It shall be fixed to alignment and securely braced to withstand, without displacement ordefection, the pressure of wet concrete while it is being cast and tamped. It shall beconstructed in such a manner that there shall be no leakage of mortar.

4.3 A gap of 15 cm shall be left between lifts, to be filled later, to facilitate the pouring ofconcrete for the lining of the next lower lift.

4.4 The surfaces of the shuttering must be free from encrustations, and must be cleaned andoiled with approved commercial oil, free from toxic substances, that will effectivelyprevent sticking and will not stain the concrete surface. Edible oil products may be usedfor this purpose, subject to the engineers’ approval.

4.5 Each lift shall have a curb at its base and at intervals as shown in the drawings.

4.6 Concrete shall be placed behind the shuttering in layers 200mm deep and air bubbles


Appendices

45

removed by rodding with a piece of reinforcing steel and by tapping the form work with ahammer.

4.7 To form watertight joints between lifts, the surface of the concrete at the top of theshuttering shall be left level but rough. About 4 hours after placement of the concrete thesurface shall be sprayed with water and brushed to expose the course aggregate.Brushing shall be carried out carefully so as not to disturb the coarse aggregate particles.The surface is wetted with a cement slurry immediately before pouring the next section oflining.

4.8 Lining shuttering shall be left in place for a minimum of 24 hours after the concrete ispoured.

Caissons4.9 Below the water table and in unstable formations above the water table, the lining shall

be made of open-ended caissons, pre-cast from concrete having a 1:2:4 mix of cement,sand and aggregates. The caissons shall have a minimum thickness of 70mm and afinished inside diameter of 0.95 metres. If caissons are used within 3 metres of thesurface, their joints and weep holes (if present) shall be sealed with cement mortar.

4.10 Caissons in the water bearing zone may optionally be cast with weep holes formed bypegs of 10 - 13mm steel rod spaced at 150mm vertical intervals (ie. Three rows per ring),and about 370mm horizontal spacing (ie. Eight equally spaced weep holes per row).Position of weep holes should staggered by a horizontal offset of 185mm in successiverows.

4.11 Weep holes must all slope upward towards the center of the ring at a minimum angle of30 degrees above horizontal.

4.12 Rebate edges shall be provided at the upper and lower edges of each caisson to providegood joints between caissons. Caissons shall be oriented so that the rebate joint slopesupward toward the centre of the well. During excavation of top of the caissons shall notbe allowed to sink below the bottom footing of cast in-situ lining. On completion of thewell the caissons shall overlap the cast in-situ lining by at least 300mm and the spacebetween the caissons and lining filled with gravel (6-19mm).

Bottom Lining4.13 The bottom of the well shall be lined with graded aggregate (6-19mm) having a minimum


Appendices

46

thickness of 15cm.

5. Depth and Yield of Completed Wells5.1 The well shall be deemed sufficiently deep, subject to the approval of the engineer, when

the nominal targets of depth and yield are met. At least 3 metres of water and a minimumyield of 10 litres per minute, or 2.5 metres of water and 15 litres per minute, or 2.0 metresof water and 20 litres per minute may be deemed the nominal targets depending on theconditions encountered. The engineer will authorise the completion of lining and headworks when these conditions and the standards of quality are met to the his satisfaction.Yield test methods are described in section 8.

5.2 In cases where hard rock prevents further progress, and at the discretion of the engineer,the nominal targets may be revised to permit the completion of a well that is deemed tobe a good potential source even though the nominal targets are not met.

5.3 The wells will be designated as “provisionally completed” until the final depth and yieldare tested at the end of the dry season. This testing will be ordered and evaluated by theengineer. At this time further deepening may be ordered by the engineer if the yield ordepth is deemed to have reduced beyond acceptable limits.

6. Headworks

Head Wall6.1 The cast in-situ or caisson lining shall be continued above ground level to form a head

wall. The height of this headwall shall be 250mm above the original ground level.

Well apron6.2 After the well lining is completed, an apron 4.75 metres x 4.75 metres, sloped (2 - 5%) to

drain radially outwards shall be constructed with curb as shown in the drawings.Excavated material low in clay content and free of organic matter shall be used to fill thevoid space on which the apron will be cast. This material shall be dampened and wellcompacted. The apron shall have a minimum thickness of 75mm and shall be made ofconcrete with a 1:2½:5 mix of cement, sand and aggregates.

6.3 The platform reduces contamination of the well by providing a surface above the groundlevel that is easier to keep clean, and a place to put containers when being filled with ahand pump. A plinth shall be constructed under the hand pump discharge on which torest the containers while filling.


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Well cover slab6.4 Wells to be fitted with hand pumps shall be provided with a cover slab as shown in the

drawings. The well cover slab shall be of 75mm thick reinforced concrete having a 1:2:4mix of cement, sand and aggregates. Reinforcement shall be with 10mm diameter (3/8inch) iron rods at 15cm spacing as shown in the drawings.

6.5 A round opening 550mm dia with a removable concrete cover shall be provided in thewell cover slab to allow access for cleaning the well. A 600mm high optional extensionshall be provided as shown in the drawings, in case the access hatch must be used fordrawing water. The joint between the cover slab and the extension shall be rebated asshown in the drawings. The access hatch and extension shall be made from a 1:2:4 mixof cement, sand and aggregates.

6.6 A second opening of 150mm diameter shall also be provided in the well cover slab forthe hand pump rising main. It also shall be bordered by a raised lip as shown in thedrawings to prevent spilled water from entering the well. A standard base plate designfor mounting an approved shallow hand pump shall be used as instructed by the ProjectManager

Drainage Channel6.7 A drainage channel shall be constructed from one corner of the well apron to collect

drainage water and then convey it to a cattle watering trough (optional) and soakaway, asis shown in the design drawings, from 1:2½:5 mix of cement, sand and aggregates.

Watering Trough (optional)6.8 A watering trough dimensioned as shown in the drawings and made from a 1:2½:5 mix of

cement, sand and aggregates shall be constructed for watering livestock.

Soakaway6.9 A soakaway shall be constructed as shown in the design drawings.


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7. Quality of Materials

Sand and aggregates7.1 Sand shall be clean, coarse-grained, river sand with a maximum grain size of 4mm. Sand

shall contain no more than 5% silt, and shall be free of soil, clay, organic matter or otherimpurities.

7.2 Aggregates shall be hard, clean and free of all organic material, and shall be well gradedbetween 6mm and 19mm in size. Samples of all aggregates shall be brought to theProject Manager for approval before delivery to the site.

Water7.3 The contractor shall provide all water needed on the site. Water used for mixing concrete

shall be clean and free from oil, salt or suspended clay.

Reinforcement Rods7.4 The reinforcing steel shall be free from oil, grease, dirt and paint. Any loose rust must be

removed before use. All reinforcement bars shall be fixed and placed as indicated in thedrawing.

Concrete7.5 No concrete shall be placed until form work, embedded parts, and surface preparation

have been approved by the Project Manager.

7.6 Batching of concrete shall be done by means of approved gauge boxes. Hand mixing ofconcrete shall be done on a mixing platform of weak concrete of at least 2.5 metresdiameter. Optionally, a portable mixing platform or mixer may be brought to the site.

7.7 Mixing shall continue until there is a uniform distribution of the materials and the mass isuniform in colour and consistency.

7.8 Concrete shall be used within thirty (30) minutes of mixing, otherwise it shall bediscarded.

7.9 Concrete shall be placed in all cases as nearly as practicable directly in its final positionand shall not be allowed to flow in a manner to cause segregation.


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7.10 Concreting shall be carried out continuously between and up to predetermined joints.

Curing7.11 All concrete head works, including the head wall, cover slab, apron, drainage channel and

watering trough shall be protected from rapid drying for 7 days by covering with heavyduty polythene sheeting, 25mm of frequently moistened sand, or the method approved bythe Project Manager.

8. Testing and Cleaning

Water Quality8.1 When ground water enters the well to a depth of 500mm a water sample shall be taken

for chemical analysis by GWSC's Community Water and Sanitation Division. If thewater quality is not acceptable the well may be abandoned.

Water Yield8.2 The well shall be tested for water yield when it has been excavated 3 metres below the

water table, or sooner as directed by the Project Manger. The yield estimation isprimarily based upon recovery rate following three hours of evacuation by pumping orbailing.

8.3 Pumping or bailing may cease after three hours whether the well has been emptied or not.The water level shall be measured and recorded when pumping ceases and every halfhour thereafter for 12 hours or until the water level is within 100mm of its startingposition. The yield estimation shall be based upon the first half hour interval measuredafter the water level exceeds the minimum depth of 0.5 metres above the bottom of thewell. The yield in litres per minute shall be calculated by dividing the estimated volumerecovered in this interval by 30.

8.4 If the recharge rate does not exceed 10 litres per minute, the Project Manager may requestthe well to be deepened. However, when working in rock the minimum requirement shallbe that the water depth rises at least 1.5 metres in 12 hours.

Cleaning and disinfection8.5 After the water yield has been measured and accepted by the Project Manager, the well

lining shall be scrubbed clean and the water bailed or pumped until it is clear. After theentire well is accepted by the Project Manager, the well shall be disinfected by dosing the


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water in the well with hypochlorite to give a concentration of 10 grams of chlorine percubic metre. During the 24 hour period after dosing, no water should be drawn from thewell. After 24 hours the well shall be pumped or bailed until the water no longer tastes ofchlorine and is clear.

9. Safety9.1 Safety helmets shall be worn by persons working in the well, and to the extent possible,

also by all workers on the construction site. Goggles and dust masks should be worn forstone cutting, and ear protectors for air hammering. First aid equipment should beavailable at the site at all times.

9.2 A rope ladder or equivalent means of ascent shall be provided so that workers mayquickly escape from the well.

9.3 Harnesses for lifting exhausted or injured personnel and for rescuers shall also beavailable at all times.

9.4 A light lifting head frame shall be provided , and all workers shall be trained in its use.

9.5 When workers are in the well at least one person shall always watch them from the top ofthe well.

9.6 There must be agreed signals for indicating if a worker is in distress and for normalworks. All workers shall be trained to use and interpret these signals.

9.7 The area around the well shall be kept clear of tools, ropes, rocks, cement bags etc.

9.8 All workmen must be aware of the possible release of poisonous gases and low oxygenlevels in wells. No smoking shall be allowed in the excavation.

9.9 Petrol and diesel pumps shall be operated downwind of the well and at least 5m from theedge of the well. Exhaust gases are heavier than air and will sink to the lowest levelspossible. Under no circumstances shall combustion engines be lowered into wells tofacilitate dewatering or for any other purpose. This leads to a build-up of carbonmonoxide which will cause the death within seconds of anyone present in the well.

9.10 At night or when work in the well has been suspended the mouth of the well shall besecurely covered.


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9.11 The tripod, winch, and cable used to place the concrete caissons in the well must bestrong enough to carry their full weight. Its capacity shall be checked by the contractor inthe presence of the Project Manager.

9.12 The use of explosives for well blasting shall only be carried out by fully competent andtrained personnel since the storage, handling, placing and detonation of explosives is adangerous operation requiring a specialist. It is crucial following the use of explosives topurge the well of all toxic fumes remaining after detonations. Locally made explosivesusing fertilizers, diesel oil, home made gun powder or similar improvisations should notbe used because of their haphazard and erratic performance.

10. Well Construction Records10.1 The contractor shall keep a works diary on the site at all times, which must be shown to

the Engineer if he requests it. The following information shall be recorded in the worksdiary on a daily basis:

� Names of workers on the site� Record of accidents� Record of visitors� Record of Rainfall� Delivery of materials to the site� Details of concrete mixes and quantities� Description of work, including depth of well excavated� Signature of engineer for all required approvals

10.2 The contractor shall also keep a well record to provide information for maintenance andconstruction of future wells.

� Strata through which the well has been sunk� The level and thickness of aquifers encountered� The depth of rock encountered (To be confirmed by the engineer)� The length of lining and caissons� Top and bottom levels of the permeable section of the shaft� Whether water enters through the side and/or bottom� Thickness of gravel lining at the bottom of the well� Mark reference point from which depth has been measured on concrete apron

with chisel.

11. Community Interaction11.1 Interaction with the community leaders regarding siting and site clearance shall be


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flexible and participatory.

11.2 The contractor shall be encouraged to make his own arrangements for hiring of locallabour.

11.3 Consultation and, where necessary, conflict resolution with the community leaders,partner organisations, etc. shall be practiced throughout the process, culminating in thehandover process.

12. DrawingsYou must have Adobe Acrobat Reader loaded in order to read the following drawings.

Appendix C The following links will open the structural drawings inPDF (Acrobat) Format


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Bill of QuantitiesThe following is a modified Bill of Quantities document extracted from a Ghana CWSD biddingdocument.

Modifications have been made to permit the following initiatives:

� To permit bidding on either in-situ cast liners, caisson liners, or both.� To permit bidding on the revised head works structure.

1. Provisional Sums

1.1 A general provision for physical contingencies (quantity overruns) may be madeby including a provisional sum in the Summary Bill of Quantities. Similarly, acontingency allowance for possible price increases should be provided as a provisionalsum in the Summary Bill of Quantities. The inclusion of such provisional sums oftenfacilitates budgetary approval by avoiding the need to request periodic supplementaryapprovals as the future need arises. Where such provisional sums or contingencyallowances are used, the Contract Data should state the manner in which they will beused, and under whose authority (usually the Project Manager’s).

1.2 The estimated cost of specialised work to be carried out, or of special goods tobe supplied, by other contractors, should be indicated in the relevant part of the Bill ofQuantities as a particular provisional sum with an appropriate brief description. Aseparate procurement procedure is normally carried out by the Employer to select suchspecialised contractors. To provide an element of competition among the bidders inrespect of any facilities, amenities, attendance, etc., to be provided by the successfulBidder as prime Contractor for the use and convenience of the specialist contractors,each related provisional sum should be followed by an item in the Bill of Quantitiesinviting the Bidder to quote a sum for such amenities, facilities, attendance, etc.

ITEM DESCRIPTION UNIT QUANTITY RATE AMOUNT

1.Mobilisation

1.a To site for well construction Each 10

1.b To site for well deepening Each 5

SUB-TOTAL I


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2.Setting up / Excavation

2.a Site Preparation Each 10

2.b Excavation above water table(0 - 4 metres)

M 40

2.c Excavation above water table(4 - 8 metres)

M 40

2.d Excavation above water table(over 8 metres)

M 20

2.e Excavation below water table(3 metres)

M 30

2.f Excavation below water table(deepening 2 metres)(Provisional)

M 10

2.g Excavation in hard rock (extrafor hard rock conditions)

M 10

SUB-TOTAL II

3.Well Lining

3.a Well Lining above the watertable (0 - 4 metres)

M 40

3.b Well Lining above the watertable (4 - 8 metres)

M 40

3.c Well Lining above the watertable (over 8 metres)

M 20

3.d Caisson Lining below thewater table (3 metres)

M 30

3.e Caisson Lining below watertable (deepening up to 2 m)(Provisional)

M 10

3.f Graded gravel inlet filter Each 10

SUB-TOTAL III


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ITEM DESCRIPTION UNIT QUANTITY RATE AMOUNT

4.Head Works

4.a Head walls Each 10

4.b Well cover slabs Each 10

4.c Access extensions Each 10

4.d Access hatch covers Each 10

4.e Aprons Each 10

4.f Drainage channel Each 10

4.g Trough and soakage pit Each 10

SUB-TOTAL IV

SUMMARYITEM ACTIVITY SUB-TOTAL

1 Mobilisation /Setting up

2 Excavation

3 Well Lining

4 Head Works

GRAND TOTAL:


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Appendix D BibliographyThe following books have inspired many previous workers in the field, including the author ofthis document. They deserve the greatest credit for their contribution to the hand dug well field.If we appear to criticise certain aspects of these works, it is with the intent of increasing theirusefulness to their readers.

1. Hand Dug Wells and Their Construction, by Watt, S.B. and Wood, W.E. (IntermediateTechnology Publications, 103/105 Southampton Row, London, UK WC1B 4HH) (1979).

This is one of the best books available on hand dug well construction. With considerablecoverage of the in-situ lining method, literally one short paragraph and one illustrationare offered on the sinking of caissons. Be wary of the proposal to use porous cement forcaissons. Such porosity, while necessary for in-situ lining, is quite unnecessary forcaisson lining, and the weakened caisson rings can be very dangerous. Add caisson-sinking tools to the equipment lists.

2. Wells Construction, Hand Dug and Hand Drilledby Brush, Richard E. (Action/PeaceCorps, Washington, D.C., USA)(1979).This is the other best book on hand dug and hand drilled wells construction. It providesthe most complete appendices on related technical issues such as concrete, pumps, watertreatment, etc. Be wary of the extremely high concentrations of chlorine recommendedfor disinfection of wells. Somewhere between a tenth and a third of these concentrationswould be sufficient and less environmentally damaging. Three full pages are dedicated tothe sinking of linings, but beware of the tools illustrated in this section. A shovel orspade has no place in caisson sinking. A short digging hoe should be substituted. Againavoid the use of porous concrete, which is unnecessary in the case of caisson liners.

3. Wells Manual - Program and Training Journaledited by Luzzato, Francis A.(Action/Peace Corps, Washington, D.C., USA) (1974).Comprised of various papers on relevant experience in well digging, this book is in manyways a predecessor of number 2 above.

4. The Construction and Maintenance of Water Wells(VITA Publications, College Campus,Schenectady, N.Y., USA)(1969)An excellent compilation of various technologies for well digging, this book has anillustrative format that is refreshing.

5. Village Technology Handbook(VITA Publications, College Campus, Schenectady, N.Y.,USA)(1970)A more generalised handbook on technologies for small rural communities in developing


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57

countries, this book is easy reading.

6. Construction of Hand-Dug Well(HELVETAS, St. Moritzstrasse 15, Postfach, CH-8042Zuerich, Switzerland)(1994).Another excellent book, this one is written as a construction manual with blueprints.Beware of the illustrations of caisson sinking which would place the worker in adangerous position below the unstabilised caisson ring. Be very wary of the porousconcrete mixture. The designs presented are interesting because they reduce the caissonwall thickness to 5 cm. This is not an undesirable change, provided that the reinforcingplacement and concrete filling can be accomplished with sufficient precision.

7. A Safe Economical Well,by Dr. E.V. Abbott, M.D, DPH. (Mimeographedreproduction)(American Friends Service Committee, Philadelphia, PA, USA)(1956)Dr Abbott introduced and refined the use of caissons in eastern India between 1952 and1956 in an area with stable soils. The document describes a specific variation of thecaisson lined well. Caisson sinking had not yet been introduced, as it was unnecessary inthis part of India.

8. Dug Wells Have a Future for Irrigation,by E.V.Abbott, MD, DPH, Hoshangabad MP,India (Mimeographed reproduction)(1963) Out of print. The Author has kindly provideda copy.An article written for the Canadian Friends’ Service Committee and the Friends’ ServiceCouncil, after the author had spent some seven years developing and refining caissonsinking techniques in central India. These articles are referenced because although thetechniques described spread rapidly and successfully in India, they were never publishedinternationally, resulting in some erroneous caissoning practices being adoptedelsewhere.

9. Preparation of Forms for Casting Concrete Well Rings,by E.V.Abbott, MD, DPH,Hoshangabad MP, India (Mimeographed reproduction)(Revised Sept1965) Out of printSee the comments on reference #8 above.

10. Method of Casting Reinforced Concrete Well Lining Rings,by E.V.Abbott, MD, DPH,Hoshangabad MP, India (Mimeographed reproduction) (Revised Sept1965) Out of printSee the comments on reference #8 above.

11. The Dug Well Subheadings: The Rasulia Type Well; The Barpali Type Well; Deepeningof Wells; Special First Ring for Use in Sand,by E.V.Abbott and Peter Stein,Hoshangabad, MP, India (Mimeographed reproduction) (1965) Out of printSee the comments on reference #8 above.


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12. Specifications and Drawings for Hand Dug Wellsby ISODEC for Community Waterand Sanitation Division, Ghana Water and Sewerage Corporation (June 1996)

13. Hand Dug Well Construction, A manual for the construction of an improved Hand DugWell (ISODEC, P.O.Box 8604, Accra North, Ghana)

Appendix E AcknowledgementsThe author would like to thank all of the authors of the above documents, the co-workers he hasworked with in the field, and most especially, Tay Awoosah, and Namps. Much appreciationalto goes to Alberto Guindon, for assistance with the editing, and to Alan Etherington forconstructive editing during several years.

Appendix F About the AuthorStephen P. Abbott, B.A.Sc, M.A.Sc, P.Eng.

Steve Abbott spent 12 years as a child and young adult in India, living, playing, and eventuallyworking alongside his father, Dr. Edwin Abbott, in dug well construction, rural sanitation, and avariety of other projects.

In 1965 the family returned to Canada. There, Steve Abbott completed his high schooleducation, and two university degrees in Mechanical Engineering, specialising in fluidmechanics, energy conversion, and solar energy topics.

In 1975 he began to travel abroad to do voluntary work in Central America. In 1983 he travelledto Africa, as technical advisor, and then team leader of a water project in Northern Ghana.

Since that time, Steve has worked on water and sanitation projects and relief efforts in Somalia,Nepal, Ghana, Alaska, Goma Zaire, Nicaragua, and Costa Rica. He has evaluated water,sanitation, and relief efforts in Ethiopia, Kenya, and Peru, and assessed drought conditions in thesemi-arid regions of Brazil.

While very much moved and motivated by refugee relief efforts, he also has a great enthusiasmfor every opportunity to teach, develop, and refine technologies in the very ancient fields of ruralwater supply and sanitation.

Steve Abbott is currently writing a book on Hand Dug Well Construction and Organisation, apart of which formed the basis for this document. The completion of that book is now expectedto happen in 2001.

Steve can be contacted by e-mail at: <[email protected]>

Hand Dug Well Manual (Abbott)

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